Unit 5: Nervous System
Unit 5: Lesson 1
Overview of the Nervous System
Nervous system can be divided anatomically and/or functionally
Anatomical divisions:
Central nervous system (CNS)
Peripheral nervous system (PNS)
Functional division
Afferent division: info to the brain
Efferent division: info from the brain
- somatic nervous system (SNS)
- Autonomic nervous system (ANS) → sympathetic and parasympathetic
Neural Tissue
2 distinct types of cells:
Neurons (nerve cells)
Basic functional unit of the nervous system
Responsible for the transfer and processing of information in the nervous system
Neuroglia
Also referred to as glial cells
Supporting cells that separate and protect neurons
Is the glue that holds the nervous system together
Supporting and protecting the nervous system
The Neuron
Nissel bodies: are in clusters, are what gives grey matter (cell bodies) its color
Dendrite: branches off of cell bodies, Intercellular communication
Axon hillock: action potential starts here, propagated down axon
Axolemma: plasma membrane around neuron, action potential moves through this membrane
Telodendria: branch at end that is in the axon/synapse terminal
Axon terminals: where the synapse is going
Dendrite → axon terminal
Myelinated nervous cells = white matter
Can be stimulated by an electrical change → excitable
Most neurons lack centrioles = no cell division , why brain/nervous injuries are so serious and long lasting
Neuroglia
Glial Cells of the CNS:
Astrocytes: neural development, you have the most of them and they are the largest, provided the structural framework, also forms scar tissue. BLOOD BRAIN BARRIER
Oligodendrocytes: myelin, wraps around the neuron (myelin in cells send messages faster, makes the myelin for the CNS
Microglia: phagocytic cells (immune), travel through nervous tissue looking for pathogens
Ependymal cells: simple ciliated cuboidal, line the ventricles in brain and central canal of spine, makes cerebrospinal fluid (CSF)
Glial Cells of the PNS:
Satellite cells
Schwann cells
Neuroglia of the PNS: Satellite & Schwann Cells
The cell bodies cluster together → creates a ganglia
Astrocytes of the PNS surrounds nervous cells
Schwann cells, responsible for creating myelin in PNS
Nursing Consideration
What happens if the myelin sheath is damaged? → things are going to slow down, demyelination is the result of diseases that attack the myelin sheath, MS
What happens when a peripheral neuron is injured? → schwann cells, pressure injury
Classification of neurons
Classified by structure and/or function
Structural classification of neurons:
Anaxonic neurons
found in brain and special sense organs; functions poorly understood
Bipolar neurons
rare; found in special sense organs
Unipolar neurons
most sensory neurons of PNS are unipolar; longest axons can extend from toes to spinal cord
Multipolar neurons
most common neuron in CNS
Functional classification of neurons:
Sensory Neurons (Taking info to CNS)
afferent fibers
send information from the PNS to the CNS
includes somatic (skeletal muscles) sensory neurons and visceral (organs) sensory neurons
Sensory receptors:
Interoceptors- monitor digestive, resp, urinary systems, sensing internal sensations
Exteroceptors- touch, temo, pressure, senses, come from outside the body
Proprioceptors- position sense, balance, knowing where body parts are
Motor Neurons
Interneurons
Ganglion → a cluster of nerve cell bodies in PNS
Classifications of neurons
Functional classification of neurons:
Sensory Neurons
Motor Neurons
efferent fibers
includes somatic motor neurons and visceral motor neurons
preganglionic vs postganglionic fibers
Interneurons (processing censor) → can be excitatory or inhibitory
most abundant type of neuron; also called association neurons
exist between sensory and motor neurons
analyze sensory input and coordinate motor output
can be excitatory or inhibitory
Synapse (communication point)
specialized site where the neuron communicates with another cell
message is transmitted from the presynaptic cell to the postsynaptic cell
postsynaptic cell may be another neuron, a muscle fiber, or a gland cell
2 types of synapses:
electrical synapse : channel proteins, fast, cardiac muscles, rare
chemical synapse: communicate via neurotransmitters
Membrane Potential
Plasma membranes have a membrane potential (difference between change) or are polarized electrically
Separation of charges across the membrane or a difference in the relative number of cations (+) and anions (-) in the ICF and ECF
Nerve and muscles cells have a specialized use for this membrane potential:
Undergo transient, rapid changes in their membrane potential
These fluctuations serve as electrical signals
Considered excitable tissues
Maintaining balance at rest
(Na+,Cl-) → ECF, more positive. (K+, proteins) → ICF, more negative
Membrane potential
Resting membrane potential
The membrane potential of a resting (@ rest it is a little bit neg), unstimulated cell
When a neuron is not conducting electrical signals, it is said to be “resting”. At rest, a neuron’s potential is – 70 mv
2 Kinds of Potential Change:
Graded potential (threshold is not met)
Temporary, localized change in resting potential
Stimulates that causes a significant movement of ions
Caused by a stimulus
Small signal; short range (one the threshold is met the message will always be sent)
Action potential (threshold is met)
Is an electrical impulse produced by graded potential
Propagates along surface of axon to synapse
Large signal; travel long distance
Action potential
a brief, rapid, and large (100 mV) change in membrane potential
occurs in response to graded potentials that meet threshold
essential for conduction of nerve impulses
threshold and “all-or-none principle” → either fires or it doesn't
propagated through entire membrane in nondecremental fashion
When threshold is met the signal will be sent from 1 end of the nerve to the other. The power and strength of the action potential will be the same for the entire length of the neuron’
Steps in Action Potential
*happens in the plasma membrane of a neuron
Depolarization to threshold
Activation of voltage-gated sodium ion channels (rapid depolarization), neuron will get more positive
Inactivation of voltage-gated sodium ion channels and activation of potassium ion channels (beginning repolarization) →sodium gate close potassium gate open
Closing of voltage-gated potassium channels (brief hyperpolarization) and a return to resting potential.
Terms to Understand:
Polarization- any state when the membrane potential is greater or less than 0 mV, one side is different than the other
Depolarization- membrane becomes less polarized than the resting potential
Repolarization (slow closing K+ gates)- membrane returns to resting potential after having been depolarized
Hyperpolarization- membrane becomes more polarized than at resting potential
Characteristic Features of Action Potentials
All-or-none law
all stimuli that bring a membrane to threshold will generate identical action potentials
no summation
All action potentials are the same intensity
Nondecremental
the last action potential has the same amplitude as the first
One way
Refractory Period
absolute refractory period: action potential has already started so new action potential can not happen. Start when Na+ gates are open, go half way through refractory period
relative refractory period: larger than normal stimulus because it is below the resting membrane potential
during repolarization (while K+ gates are open)
Propagation of Action Potential
Action potentials are propagated from the axon hillock (trigger zone) to the axon terminals
Two types of propagation:
Continuous Propagation
conduction in unmyelinated fibers
action potential spreads along every portion of the membrane by depolarizing adjacent regions down the length of the axon
Saltatory Propagation:
rapid conduction in myelinated fibers
impulse jumps over sections of the fiber that are covered by insulating myelin
Synapse (more)
Electrical Synapses
presynaptic and postsynaptic membranes are linked by gap junctions
ions pass between cells through pores and action potentials are propagated quickly
electrical synapses are rare; found in retina and some parts of cerebral cortex, and ciliary ganglia
Found mostly in heart
Transmembrane proteins =gap junctions
Chemical Synapse
Most common type of synapse between neurons; only type pf synapse between neurons and other cells
Cells separate by synaptic cleft; presynaptic cell sends the message and postsynaptic cell receives it
Involve neurotransmitters
Cell to… muscle,cell,gland
Types of chemical synapses:
Neuromuscular junction: synapse between neuron and skeletal muscle ce;;
Neuroglandular junction: synapse between neuron and gland cell
Neurotransmitters
Chemical compounds (in synaptic vesicles) released by one neuron to affect the membrane potential of another
Neurotransmitters are:
released into synaptic cleft and exert their effect on receptors in postsynaptic membrane
broken down by enzymes, reabsorbed
Travel from presynaptic → postsynaptic
Excitatory → promotes the action potential/ start polarization
Inhibitory → hyperpolarization stops the action potential
Neuromodulator: impact the sensitivity of the next cell to the neurotransmitter that is going to act on it
Neurotransmitter Release
Action potential passes along axons and over synaptic knob/terminal
Synaptic terminals (Knobs) become more permeable to calcium ions, which diffuse inward
Synaptic vesicles fuse to terminal membranes
Synaptic vesicles release neurotransmitters into the synaptic cleft
Synaptic vesicles re-enter axon’s cytoplasm to pick up more neurotransmitters.(if they are not used they either got broken down or are taken back up by the presynaptic membrane)
Classification of Neurotransmitters
Excitatory Neurotransmitters
cause depolarization of postsynaptic membrane and promote generation of action potential
Inhibitory Neurotransmitters
cause hyperpolarization of postsynaptic membrane and suppress generation of action potential
What about neurotransmitters like acetylcholine (ACh) that can be both excitatory and inhibitory? Depends on the receptor → receptor decided which one
Major Classes of Neurotransmitters
Biogenic Amines
Amino Acids
Neuropeptides
Dissolved gasses
Biological Amines
Have to do with behavior, movement, temperature, emotion
Remember: Catecholamines → hormones made by adrenal glands (norepinephrine, epinephrine, dopamine)
adrenergic : has to do with adrenaline (serotonin, histamine), binds with NE
Norepinephrine (NE)
Released by adrenergic synapses
Excitatory and depolarizing effect
Widely distributed in brain and portions of ANS
Dopamine (feel good hormone)
A CNS neurotransmitter
May be excitatory or inhibitory
Involved in Parkinson’s disease (too little dopamine) and cocaine use
Serotonin
CNS neurotransmitter
Affects attention and emotional states
Amino Acids
Glutamate - works with brain for memory, most abundant excitatory neurotransmitter
Aspartate - voluntary muscle control
Glycine - inhibitory, control motor movements
Gamma-aminobutyric acid (GABA)- too much sleepy, brain slows down
Inhibitory effect
Functions in CNS are not fully understood: opens Cl- channels → when opened it will change polarity and inhibit/ slow the transmission of nerve impulses in CNS
Epilepsy, mood, relaxation, sleep
Neuropeptides
small peptide chains; synthesized and released by axon terminal
includes a group of neuromodulators called endogenous opioids → pain relieving drugs
bind to same receptors as substances like morphine or opium
primary function is pain relief by inhibiting Substance P (things in the body that are able to block substance P) (neurotransmitter important for pain sensation)
Enkephalins,endorphins “runners high”, dynorphins
Dissolved Gases
Lipid soluble gases → easier time crossing membrane. It doesnt need help to cross
Nitric Oxide (NO)
from axon terminals in several regions of the brain and in smooth muscle of blood vessel walls
Carbon Monoxide (CO)
function poorly understood
Hemoglobin highly prefers this
What is Post-synaptic potential (PSP)
refers to a response/change in the membrane potential at the postsynaptic membrane
2 types:
Excitatory postsynaptic potential (EPSP)
synapse responds to neurotransmitter with excitatory response (depolarization); promotes generation of action potential.
What are some examples of excitatory neurotransmitters?
Inhibitory postsynaptic potential (IPSP)
synapse responds to neurotransmitter with inhibitory response; causes hyperpolarization and suppresses the generation of action potential
Unit 5: Lesson 2- Central Nervous System
Includes the:
spinal cord & spinal nerves
brain & cranial nerve
Anatomy of the Spinal Cord (made of mainly nervous tissue)
4 regions
31 segments (each with a pair of spinal nerves)
composed of grey (cell bodies) and white matter (myelinated axons)
structures to note:
posterior median sulcus
anterior median fissure
central canal
conus medullaris
filum terminale
cauda equina
Protection
There are numerous layers of protection surrounding the spinal cord. Nervous tissue can easily be replenished
Epidural space: from the bone to the first meningeal layer → exchange of nutrient and lots of blood vessels
3 Spinal Meninges:
Dura Mater: fibrous, collagen, continuous from protecting, brain and spinal cord, anchors brain and bottom
Arachnoid Mater: in direct contact with the dura mater (no space between the two in the spinal cord (but you in brain))
subarachnoid space: full of CSF. B vessels, space where spinal anestinesia is placed
Pia Mater
Clinical Application → Lumbar Puncture
Technique
long needle into subarachnoid space
safe from L3 to L5 (safe because there is no spinal cord)
Purpose
sampling cerebrospinal fluid (CSF) for diagnosis
injection of antibiotics, anesthetics or chemotherapy
measurement of CSF pressure
Spinal Roots & Ganglia
roots= axons
ventral(anterior)=dorsal (posterior)
ganglia= cell bodies
every spinal segment is associated with a pair of spinal ganglia (which hold the cell bodies of sensory neurons)
Posterior Root (dorsal/sensory root)
sensory neuron axons (bringing info to the CNS)
Posterior root ganglion contains cell bodies of sensory neurons
Anterior Root (ventral/motor root)
motor neuron axons (take info from CNS to effectors in PNS)
The posterior and anterior roots pass through the intervertebral foramen and join together to form a single spinal nerve
In through the posterior out through anterior
Spinal Nerve
There are 31 pairs of spinal nerves
8 cervical nerves
Note: All 8 cervical nerves exit the spinal column above their vertebrae
C1 exits the spinal column above the C1 vertebrae
C4 nerve is superior to C4 vertebrae
C1 → C7 leave above spinal cord
C8(extra) nerve exits above T1 vertebrae
12 thoracic nerves
Note: Starting at the T1 spinal nerve, spinal nerves exit the spinal column below their vertebrae
T1 nerve is inferior to T1 vertebrae
L2 nerve is inferior to L1 vertebrae
5 lumbar nerves; 5 sacral nerves; 1 coccygeal nerve
Mixed nerve: a nerve that has both sensory and motor neurons
Peripheral Distribution of Spinal Nerves
Outside the spinal cord, spinal nerves branch to carry motor and/or sensory information between the CNS and PNS
What is a ramus? A passageway, decides what way the direction the nerve will go, determines what the nerve will go, determines what the nerve is going to innervate (mixed nerve)
Posterior (dorsal) ramus: heading to back
Anterior (ventral) ramus : heading to front, take motor and sensory from body to brian
Rami communicantes (in T1-L2)
predominantly serve the sympathetic nervous system
Spinal nerves supply specific regions of the skin known as dermatomes
White matter
Grey matter contains neuronal cell bodies, dendrites and nerve synapses
White matter contains the axons of nerve fibers
White matter is arranged into columns and tracts
Anterior white columns connect at the anterior white commissure
Tract→ axons that have a similar function are put in a tract then put in a column
Decasation → moving one side to another
Dermatomes
A sensory region that is monitored by a single spinal segment
Is damaged will lose sensation tm parts of body
Shingles → impacts specific dermatomes of the spine
Nerve Plexuses
What is a nerve plexus?
There are four spinal nerve plexuses:
Cervical plexus: head neck shoulders, phrenic (diaphragm) nerve, (hiccups twitch in phrenic nerve)
Brachial plexus: if injured whole shoulder, arm, hand, will go numb. Think when you sleep on arm
Lumbar plexus: genitals, butt
Sacral plexus: genitals, butt
Refer to Figure 13-9
Reflexers
What is a Reflex?
An immediate involuntary motor response, nto aware of it in the moment
What is a Reflex Arc?
The neural “wiring” of a single reflex; begins at a sensory receptor and ends at a peripheral effector (eg. muscle fiber or gland)
Spinal reflexes can be:
Monosynaptic
Involves a single segment of the spinal cord
Example: Patellar Reflex
Polysynaptic (involves more than one nerve)
Integrates motor output from several spinal segments
Example: Withdrawal Reflex (from heat, ex. Touching stove)
Reflex Arch
Activation of a sensory receptor
Activation of sensory neuron (and relay of information to the CNS)
Information processing in the CNS
Activation of a motor neuron
Response by the peripheral effector
Clinical Application:
Lack of reflex → something wrong in CNS
Plantar reflex: normal in adults, stroke lateral sole, causes redlexive toe-curling
The babinski reflex: normal in infants, may indicate CNS damage in adults
4 major regions of the brain:
Cerebrum (cerebral hemispheres)
Cerebellum: mini brain
Diencephalon: where hypothalamus, thalamus
Brainstem: midbrain, pons, medulla oblongata
Cerebrum
largest portion of the brain
processes sensory and motor input
responsible for conscious thought, complex movements, memory, and intellect
What is hemispheric lateralization?
Cerebral cortex → grey matter that covers the entire brain, it goes into all the clips
White Matter of the Cerebrum
Association fibers
connect areas within the same hemisphere
includes arcuate (short) and longitudinal (long)fibers
Fibers in same side of brain can communicate
Commissural fibers (left and right)
connect the two hemispheres
corpus callosum ( tiny but vert very important)& anterior commissure
Projection fibers
connect cerebrum to spinal cord and other regions of the brain
The Basal Nuclei
Cluster of cell bodies in the brain (white matter in the brain)
ivolved in subconscious control of skeletal muscle tone and learned movements (walking, writing)
inhibited by dopamine
Mostly inhibitory, produced by midbrain + inhibits movements
Controls the movement
Without the basal nuclei will go crazy → you will not be able to control movements and its hard to control the movement
Specialized Areas
cortex contains sensory areas and motor areas, separated by the central sulcus
association areas coordinate incoming and outgoing information
cortex of one hemisphere receives sensory info from, and sends motor info to, the opposite side of the body (decussation: cortex on left is receiving info from right body and vise versa)
Specialized Language Areas (stroke)
Wernicke’s Area
associated with language comprehension and speech
By authority complex in temporal lobe
Broca’s area
associated with speech production
Coordinate breathing and muscles to be able to speak
Aphasia→ language disroder caused by a damaged part of the brain
The cerebellum
second largest part of the brain
Autonomic process center for track of nerve fibers
Functions:
adjusting postural muscles of body
coordinating and adjusting complex motor patterns
Important structures:
cerebellar cortex (covers the cerebellum)
Purkinje cell layer: busiest nervous cell bodies in the whole body
Arbor vitae = “tree of life”
cerebellar nuclei
Learnerd movements, coordination
When damaged “ATAXIA” (lack of order)
The diencephalon
Surrounds 3rd ventricle
Contains the thalamus, hypothalamus, and epithalamus (pineal gland, makes melatonin)
The Thalamus
Final relay point for sensory info going to the cerebral cortex
If info doesn't pass thalamus then you wont ever be conscious of it
The hypothalamus
Functions:
Secretion of hormones
antidiuretic hormone (ADH): tells you not to pee, when thus increases so does BP because there is more pressure
Oxytocin: uterus contractions
Regulation of body temperature
Control of autonomic function: heart rate, BP, breathing, sleep wake cycle, full tummy
Coordination of voluntary and autonomic functions
Coordination of nervous and endocrine functions (via pituitary gland)
Regulation of circadian rhythms
Subconscious control of skeletal muscle contraction
Production of emotional and behavioral drives (thirst, satiety)
The Limbic System
Memory and emotion
Functional area (not a distinct physical area)
Nuclei (grey matter) and white matter tracts
Motivation
Pain → chronic pain, the emotional side
Ventricles
Neural tube left from embryonic development, this tube is left in the brain and contain CSF
Ependymal cells make CSF
Always filled with CSF
Support & Protection
Support and protection of the brain involves:
Bones of the skull (protect brain)
Parietal, frontal, occipital, and temporal bones
Cranial meninges (surround brain)
Dura mater, arachnoid mater, and pia mater
Cerebrospinal fluid
Blood–brain barrier
Cranial Meninges
Includes the:
Dura mater (fused with outer skull)
fused with periosteum of cranial bones
dural folds; dural sinuses: dips into brain for more protection
Arachnoid mater: **Should not be any space
arachnoid trabeculae
subarachnoid space
Spiderweb like
Pia mater (innermost)
lines the brain
anchored by astrocyte projections
Lots of blood vessels
continuous with spinal meninges
no epidural space
Clinical Applications:
Meningitis
infection or inflammation of the meninges
Hemorrhage (active bleeding) or Hematoma (pool of mostly clotted blood)
named according to anatomical location
Where would a subarachnoid hemorrhage occur?
Where would a subdural hematoma occur?
Cerebrospinal Fluid (CSF)
Functions of CSF:
Supports the brain
Cushions the brain and spinal cord
Transports nutrients, chemical messengers, and wastes
Formation of CSF:
Produced by the ependymal cells of the choroid plexus
They actively transport nutrients, vitamins, and ions into the CSF and actively remove waste from the CSF
Circulation of CSF:
created in choroid plexus of lateral ventricles → interventricular foramen to third ventricle → aqueduct of midbrain to fourth ventricle → arachnoid granulations to regular circulation
Blood Brain Barrier
Isolates the CNS from the general circulation
3 protective segments:
endothelial cells with tight junctions
basement membrane
Astrocytes → make this barrier
Transport across the barrier is HIGHLY selective
Intact throughout CNS, with exception of circumventricular organs with fenestrated capillaries that allow necessary link for neuroendocrine functions.
Lots of tight junctions → almost impossible
Cranial Nerves (CN)
12 pairs of cranial nerves
numbered from CN I to CN XII
10 cranial nerves originate in brainstem
olfactory nerve (CN I) attaches to cerebrum
Optic nerve (CN II) attaches to diencephalon
Review pages 495-505 → know the name, number and function of the cranial nerve
Unit 5: Lesson 3- Sensory and motor pathways
Afferent Pathway:
carries sensory information from sensory receptors in PNS to Central Nervous System
includes the somatic and visceral sensory pathways:
somatic sensory → somatosensory cortex
visceral sensory → brainstem & diencephalon (reflex centers)
Efferent Pathway:
carries motor commands from the CNS to PNS
somatic motor pathways (skin, joints, ect) → motor commands to skeletal muscles
autonomic pathways (organs)→ includes sympathetic and parasympathetic NS, never makes it way to the cerebral cortex
1% of sensations make it to your consciousness
General Sensory Receptors
What is a sensory receptor? Cells that are monitored by receptors or cells that are monitoring receptors
Receptor specificity → not a receptors will react to all types of stimuli
Exteroceptors
Provide information about external environment
Proprioceptors
Report positions of skeletal muscles and joints
Interoceptors
Monitor visceral organs and functions
What is the difference between sensation and perception? All info is sensed but not all is perceived to your conscious awareness
Sensory Reception
Receptor Specificity
free nerve endings show little receptor specificity
Receptive Field
the area monitored by a single receptor and more sensitive, smaller area means you can pinpoint exactly where the receptor is
smaller receptive field = better localization of stimuli
Transduction (how a stimulus is translated)
the process of converting a stimulus into an action potential that can be propagated to the CNS
Large fields=less sensation
Stimulus → threshold reached → depolarization → action potential generated → neurotransmission → axons in spinal tracts carry info to specialized areas of brain
Classifications of Sensory Receptors
Nociceptors (pain)
Thermoreceptors (temperature)
Mechanoreceptors (physical distortion)
Tactile Receptors
Baroreceptors: notice stretch
Proprioceptors: notice chemical changed
Chemoreceptors (chemical concentration): receptor specificity → dependant on nerve protection
Less sensitive overtime, responds to change
Phasic receptors:respond quickly if there is a change in stimulus or it starts. Not always responding becomes less sensitive over time. Ex. when you walk in a cold room and you get used to it
Tonic Receptors: always active never become numb or desensitized to a stimulus. Ex. balance receptors in your ear
Nociceptors
pain receptors
found in superficial skin, periosteum of bones, blood vessel walls; fewer in visceral organs
different nociceptors may be sensitive to chemical stimuli, mechanical stimuli, or temperature, pressure
nociceptors are tonic receptors, but pain perception (the pain receptors will continue to sense the pain but might not always perceive the pain the same overtime) can be modified
sensory neurons release neurotransmitters substance P and glutamate
Pain
Fast pain (poking finger on tac)(myelinated A fibers, quick fibers, fast) ⇒ sharp, “prickling” pain
often triggers reflex
Slow pain (aching lower pain)(unmyelinated C fibers, slow fibers) ⇒ aching, burning pain
Pain Pathway:
nociceptor → A or C fibers (1st order neuron) → spinal nerve → dorsal root & ganglion → neurotransmitters → 2nd order neuron decussates (crossing over to the other side of brain/spinal cord) → ascends via spinothalamic tract → thalamus → synapse with 3rd order neuron → somatosensory cortex (awareness & localization)
efferent pathway impacted by neuromodulators (endorphins, enkephalins) that modulate pain perception and
ALWAYS ENTER THROUGH POSTERIOR HORN
Thermoreceptors
temperature receptors
non-specialized, free nerve endings (not very specialized or protected)
phasic (get used to the stimuli) receptors (sensitive to change)
embedded in skin and certain organs
Follows the same pathway as pain
temperature sensations conducted along same pathways as pain sensation
Mechanoreceptors
Mechanically gated ion channels in plasma membranes open and close in response to physical distortion (stress)
When distorted the Na+ gates will open and action potential will start
Includes tactile receptors, baroreceptors, and proprioceptors
Tactile receptors
sense touch, pressure, vibration
fine (touching tip of finger) VS crude touch and pressure receptors
includes free nerve endings, root hair plexus (tight ponytail), tactile discs (finger tips), bulbous (Ruffini, low frequency vibrations) corpuscles , lamellar (Pacinian) corpuscles, tactile (fine touch, delicate) (Meissner, low frequency location) corpuscles(eyelids, lips, external genitalia) (see Figure 15-4)
Baroreceptors:
Monitor for changes in pressure
Free nerve ending (exist in very specific parts of body) within walls of distensible organs (ex. Blood vessels; portions of respiratory, digestobe, urinary tract)
Dendrites detect stretch
Detection of changes in blood pressure
Proprioceptors
position sense , balance, coordination
proprioception is a somatic sensation, exist in the somatic (aware of it)tissue its just cause they aren't in the visceral tissue so they have to be somatic
continuously sending information to the CNS
Chemoreceptors
detect small changes in concentration of dissolved chemicals
exhibit peripheral adaptation
in general senses, information from chemoreceptors does not go to primary somatosensory cortex (no conscious awareness)
Example: pH and CO2 monitoring , makes sure homeostasis is maintained
1st, 2nd, 3rd order neurons
Sensory pathways include first, second, and third-order (take stimulus to consciousness) neurons
First-order neuron
a sensory nerve that delivers sensations directly to the CNS
Second-order neuron
interneuron located at the spinal cord or brainstem
message must be passed to third-order neuron for awareness of sensation
Third-order neuron
Decussation
point at which second order neuron crosses to opposite side of CNS
Homunculus
More sensitive = more area on hommuncullus
Ex. tongue has a big chunk, is like a map of sensation in the body
Sensory pathways
Somatic sensory pathways carry sensory information from skin and muscles of body wall, head, neck, and limbs to the CNS.
Major somatic sensory pathways:
Spinothalamic pathway
conscious sensation of pain, temperature, crude touch (hard to touch
1st order neurons synapse with 2nd order in posterior horn ⇒ decussate before ascending to thalamus ⇒ 3rd order neuron to primary somatosensory cortex
Decussate- cross over at different spots
Posterior column pathway
sensation of fine touch (tactile) , pressure, vibration, and proprioception
dorsal column medial lemniscus (DCML) pathway
ascends on same side to medulla ⇒ synapses with 2nd order neuron and decussates ⇒ ends at primary somatosensory cortex
Spinocerebellar pathway
delivers proprioceptive information from skeletal muscles, tendons and joints to the cerebellum (not aware, purkinje cells) (Purkinje cells of the cerebellar cortex)
Questions: Are we consciously aware of these sensations? Why or why not?
No matter which pathway they will enter through the dorsal through the posterior horn
Clinical application
Referred Pain
when visceral (strong pain) sensation presents as somatic pain
related to autonomic and somatic nerves travelling together in well-defined dermatomal patterns
Pain is so strong that neurons are just being fired everywhere because it is so intense
example: liver pain felt in right shoulder or neck; heart pain in the left arm
2. Phantom limb pain
Pain gate theory
Initiates an action potential/stimulus that is different and hopefully going to overpower the pain receptors
Why if you wac your hand with a hammer you can squeeze it and it feels better for a bit
Visceral Sensory Pathway
information received from interoceptors of visceral organs and tissues
first-order neurons → second-order neurons in spinothalamic pathway → solitary nucleus of medulla oblongata → specific centers (respiratory center, cardiovascular center, reticular formation)
No third-order neurons
information does not reach primary somatosensory cortex
no conscious awareness of these sensations
Somatic nervous system & somatic (efferent) motor pathways
Somatic motor pathways always involve at least 2 motor neurons
upper motor neuron - the cell body is in the process center of the CNS, to either spinal cord/ other nerves
lower motor neuron- the axon of this in the CNS is leaving to wherever it needs to go
only the axon of the lower neuron extends outside the CNS
Motor unit- group of nerve fibers
Motor commands travel by motor pathways:
Corticospinal pathway- pyramidal, voluntary muscle conscious
Medial pathway (extrapyramidal, nonvoluntary, subconscious)& Lateral pathway
Both are considered somatic because they go to skeletal muscle
Corticospinal Pathway
pyramidal system (voluntary, you are aware)
conscious/voluntary movement
includes 3 tracts:
corticobulbar tract- fibers that innervate the facial muscles (cranial nerves)
lateral corticospinal tract- where they decided to decussate
anterior corticospinal tract- where they decides to decussate
Most fibers decussate in the medulla oblngata
Medial and lateral pathways
Extrapyramidal system; subconscious movement
Motor commands from the cerebrum, diencephalon, and brainstem
Medial Pathway:
muscle tone and gross movements of neck, trunk and proximal limb muscles
includes vestibulospinal tracts (posture & balance), tectospinal tracts (reflexive responses to visual and auditory stimuli), reticulospinal tracts (reflex activity) going to head
Hast to do with balance
Lateral Pathway:
muscle tone in distal limb muscles and precise movements
descend in rubrospinal tracts
Has to do with balance, differ in where they are taking the info to
Basal Nuclei and Cerebellum
Responsible for coordination and feedback control over muscle contractions
Basal nuclei → works on messages from upper motor neurons
Adjust or establish patterns of movement
Provide background patterns of movement involved in voluntary motor activities
Interneurons in basal nuclei:
stimulate neurons by releasing acetylcholine (ACh); inhibit neurons by releasing GABA
Cerebellum → has to do with practice, (ex. instruments)
monitors proprioceptive (position) sensations, visual information, and vestibular (balance) sensations from internal ear
Fine-tuning of complex movements improves with practice
allows for efficient, smooth, precisely controlled movements
Unit 5: Lesson 4- Autonomic Nervous System
ANS functions outside of our conscious awareness
Involuntary control of major body functions for homeostasis:
cardiovascular, respiratory, digestive (smooth muscle), endocrine (glands), urinary, reproductive, electrolyte, water & gas concentrations, adipose tissue (energy storage)
Directed by hypothalamus → primary, control center, relies on neurotransmitters
ANS continuously works to maintain autonomic tone (Stimulation to organs/ visceral tissue) is never turned off
ANS directs visceral reflex (maintaining homeostasis, non skeletal muscle reflex) responses
Divided into the sympathetic and parasympathetic NS
At rest → Parasympathetic NS prevails (rest and digest)
In crisis → Sympathetic NS prevails (fight or fligh)
Somatic vs autonomic nervous system
SOMATIC NERVOUS SYSTEM
consciously perceived sensations
All about skeletal muscles
motor neurons carry info from CNS to skeletal muscles
one motor neuron (lower motor neuron) connects CNS to effector
AUTONOMIC NERVOUS SYSTEM
involuntary inhibition or excitation of smooth muscle, cardiac muscle or glandular secretion
Other muscles
motor neurons carry info to visceral motor neurons in autonomic ganglia and then to visceral effectors
two motor neurons needed to connect CNS to effector/organ
Preganglionic- myelinated, faster, cluster of cell bodies outside of the CNS
postganglionic neurons- unmyelinated, slower, carries automic messages to the visceral effectors
Makes schwann cells (myelin in the PNS), and oligodendrocytes (myelin in the CNS)
Anatomy of ANS
Preganglionic neuron
cell body in brain or spinal cord
axon is myelinated fiber (Type B Fiber) that extends to the autonomic ganglion
Postganglionic neuron
cell body lies outside CNS in an autonomic ganglion
axon is unmyelinated fiber (Type C Fiber) that terminates in a visceral effector
Divisions of the ANS
2 major divisions:
Sympathetic NS
aka thoracolumbar division → location of preganglionic fibers, where the fibers start
preganglionic cell bodies in T1-L2 segments of spinal cord
short preganglionic fibers
Parasympathetic NS
aka craniosacral division → location of preganglionic fibers, where the fibers start
preganglionic cell bodies in 4 cranial nerves (3,7,9,10) and the S2-S4 segments of spinal cord
long preganglionic fibers
Note: most organs are innervated by both branches to maintain homeostasis (Exceptions: arteries, sweat glands, arrector pili muscles)
Sympathetic NS
Fight-or-Flight
Activation of the sympathetic NS →
increased mental alertness
increased metabolic rate
decreased urinary and digestive functions
activation of energy reserves
increased respiratory rate and bronchodilation
increased heart rate and blood pressure
activation of sweat glands
Increased metabolic rate, need to get rid of that extra heat
Pupils dilate, more light in
Preganglionic neurons will synapse in one of three locations:
Sympathetic Chain Ganglia (paravertebral ganglia) → effectors in body wall, thoracic cavity, head, neck, limbs
Collateral Ganglia → innervate abdominopelvic tissues and viscera
Adrenal Medulla → secrete neurotransmitters directly into bloodstream (no synapse; neurotransmitters act as hormone
Collateral Ganglia
There are three collateral ganglia
Celiac ganglion
Innervates stomach, duodenum, liver, gallbladder, pancreas, spleen, and kidney
Headed to the viscera in your abdominopelvic area
Superior mesenteric ganglion
Innervates small intestine and initial segments of large intestine
Inferior mesenteric ganglion
Innervates terminal portions of large intestine, the kidney, urinary bladder, and sex organs
Adrenal Medulla Pathway
secretes epinephrine and norepinephrine (NE) into bloodstream
80% epinephrine
epinephrine and norepinephrine travel through bloodstream (can work for a muck longer time) and can impact metabolic activity throughout body\nerve transmitters go to the blood, work like hormones because they can reach parts all over the body because its in the blood
longer lasting effects compared to direct sympathetic innervation (and neurotransmitters at synapse)
Neurotransmitters
Acetylcholine (ACh)
released from sympathetic & parasympathetic preganglionic neurons
released from parasympathetic postganglionic neurons
synapses that use ACh as neurotransmitter → cholinergic (a receptor or synapse that has acetylcholine)
excitatory effect
Norepinephrine (NE)
released from most post ganglionic neurons
neurons that release NE → adrenergic (receptor or synapse that has norepiniferine)
a catecholamine (as are epinephrine, dopamine)
effects last significantly longer than ACh (NE is in the blood)
binds to adrenergic receptors (alpha & beta receptors)
Sympathetic NS and Blood Pressure
epinephrine is non-selective, not picky
norepinephrine has higher affinity for alpha receptors, picky
Parasympathetic NS
Rest & Digest
Opposite of sympathetic, opposing action
Cranian nerve 10 (CN X) controls 75% of parasympathetic
Activation of the parasympathetic NS →
decreased metabolic rate
decreased heart rate and blood pressure
increased saliva and digestive secretions
increased digestive motility
stimulation of urination & defecation
ACh released from parasympathetic preganglionic and postganglionic neurons
2 kinds of cholinergic (reciving ACh) receptors:
Nicotinic Receptors (excitatory)
are cell bodies of sympathetic and parasympathetic postganglionic neurons
ACh activates receptor → gated Na+ channels open → excitation
Muscarinic Receptors
are in effector tissues (at neuromuscular and neuroglandular junctions of PNS) not nerve to nerve
Can be excitatory or inhibitory
innervated by parasympathetic postganglionic neurons (in smooth muscle, cardiac muscle, glands)
Dual Innervation
Organs with dual innervation receive input from the sympathetic and parasympathetic divisions (effects are typically antagonistic)
Start at different places but can target the same thing
Parasympathetic and sympathetic nerves intermingle in thoracic and abdominopelvic cavities to form autonomic plexuses.
cardiac plexus, pulmonary plexus, esophageal plexus, celiac plexus, inferior mesenteric plexus, hypogastric plexus
Refer to Figure 16-6
Exceptions to dual innervation:
most arterioles and veins→ sympathetic only
most sweat glands → sympathetic only
salivary glands → innervated by both, but not antagonistic (both stimulate secretion), both will stimulate parasympathetic (liquidy, watery saliva, drool) and sympathetic (changes composition, thicker)
Visceral reflexes
Provide autonomic motor responses to:
Modify or facilitate higher centers
All visceral reflexes are polysynaptic (more than one synapse)
Reflex arch that causes non skeletal reaction (organs, visceral)
Reflexes can be:
Long reflexes → more synapse
Short reflexes → bypasses the CNS all together
Autonomic reflex arc
Higher Order function
Higher order functions share 3 characteristics:
Require the cerebral cortex
Involve conscious and unconscious information processing
Subject to adjustment over time, will change and adapt (not innate, born with it or fixed)
Examples:
Memory
Language
Consciousness
Memory
Storage of acquired knowledge for later recall
Short-term memory: limited capacity, only a few hours, forgotten easily
Long-term memory: large capacity
Cerebral cortex, cerebellum, basal nuclei } need help from nall of these
Amygdala hippocampus: vital for memory consolidation, if damaged it is hard to make new long term memories but the existing memories stay
Memory Consolidation
Process of transferring and fixing short-term memory traces into long-term memory stores
Storing memories, repetition →long term
Engram: a single memory
Consciousness
What is consciousness?
States of consciousness: Sleep & Arousal
Sleep:
Sleep is needed for regeneration of tissues
Deep Sleep= non-REM sleep
minimal cerebral cortex activity (no dreaming); whole body relaxation; decreased HR, BP, respiratory rate
REM Sleep= dream-state
BP and respiratory rate fluctuate
Coma - not arousable with normal stimulation
Arousal
Consciousness and arousal involve complex interactions between reticular formation and cerebral cortex.
Reticular Activating System (RAS)
widespread network of interconnected neurons that extends from medulla oblongata to midbrain, send messages to activate brain
stimulation activates cerebral cortex (ends sleep and promotes cortical awareness)
collaborates with thalamic nuclei → enhanced alertness & focus
consciousness maintained by positive feedback activity
if NOT active → decreased function of cerebral cortex → unconsciousness
Language
Language
is a complex form of communication in which written or spoken words symbolize objects and convey ideas
Broca’s area (motor)
in the left frontal lobe
controls the muscles necessary for articulation; speaking ability
Wernicke’s area (sensory)
left parietal-temporal-occipital lobe
concerned with understanding both spoken and written language; language comprehension
for formulating coherent patterns of speech
Afasia: lack of ability to speak
Effects of Aging
↓ size and weight of brain
↓ number of neurons
↓ blood flow to the brain
changes in synaptic organization of brain
intracellular and extracellular changes in neurons
tangles
Plaques:alzheimers, accumulation of bad prteins
Anatomical changes can lead to functional changes:
Memory consolidation becomes more difficult
Hearing, balance, vision, smell, and taste become less acute
Reaction times are slowed
Reflexes weaken or disappear
Precision of motor control decreases
Motor patterns take longer to perform
Unit 5- Lesson 5: Special Senses
Olfaction
What are the 3 types of cells found in the olfactory epithelium
Olfactory sensory neurons, supporting cells, regenerative basal epithelial cells (STEM)
What is unique about the dendrites of olfactory sensory receptors?
The tip of the dendrites go beyond the epithelial surface , the receptor proteins exposed to outside environment
What is unique about the regenerative basal epithelial cells found in the olfactory epithelium?
Neuronal replacement: they are precursors to ner olfactory cells, means that these neurons can be replaced (rare)
What is the proper term for molecules that stimulate olfactory receptors?
Oderants: in order for us to smell a substance an orderant must be volatile enough that some of its molecules are going to enter the nose, need to be water soluble
Complete the following sentence: Olfactory stimulation is the only type of sensory information that reaches the cerebral cortex directly
What does this mean and how does it differ from other senses?
Doesnt pass through the thalamus like all the other sense do
Why does our sense of smell change as we age?
The number of neurons involved will decline leading to a decrease in sensitivity of smell
Gustation
What are the 4 functions of the gustatory system?
Protection, encouraging saliva production, sends messages to increase gastric motility, production of digestive enzymes, increase insulin release
Where are the sensory structures of the tongue (“taste buds”) located?
They are projections on the tongue called lingual papillae. In these papilla are what house the sensory structures (taste buds). Taste buds are mature gustatory epithelial cells. They are chemoreceptors
What is the proper term for molecules that stimulate gustatory receptors?
Are chemoreceptors, called tastants (dissolved food particles)
What is a “taste pore”?
Out taste buds have openings called taste pores, parts of the food dissolved in saliva come into contact with taste receptors
Trace the pathway of a taste sensation from the taste bud to the CNS. Where is the gustatory area of the cerebral cortex located?
Taste buds (CN VII, IX, X) → sensory fibers carry info to the solitary nucleus of medulla →join with other axons go to the thalamus (synapse) → info goes to the gustatory area of the cortex in the insula.
Insula: ribbon of grey matter that is just under the lateral brain surface, separates the inferior parietal cortex from the temporal lobe
Why does taste sensitivity decrease with age?
Taste buds only have a lifespan of about 10 days. The number of functional taste buds that we have decrease (decrease sensitivity)
What are the 5 categories of “tastes” that we recognize? (thought to be detected in different areas of our tongue)
Sweet (fron), salty (front side), bitter (back), sour (back side), umami (savory, meaty, many)
Vision
Identify the location and function of the following anatomical structures of the eye:
Sclera: tough outer layer of connective tissue that forms the white part of the eye
Cornea: at front anterior transparent outer layer, light rays are going to pass through first
Choroid: under sclera, contains blood vessels that nourish the retina
Ciliary body: what produces the aqueous humor ( clear liquid that fills the anterior eye)
Iris: colored part, responsible for how much light is allowed to enter the eye by adjusting the size of the pupil
Retina: where we find rods and cones (light detecting cells)
Pupil: round opening that light passes through
Lens:a clear, curved structure at the front of the eye behind the pupil. It focuses light rays that enter the eye through the pupil,
Aqueous humour: between the lens and cornea, made by ciliary bodies, fluid substance that carries nutrients to the cornea and lens
Vitreous humour: gel like substance that helps maintain that spherical shape.
Which cranial nerve and muscles are responsible for constriction and dilation of the pupil?
CN III, oculomotor
During the fight-or-flight response, will the pupils dilate or constrict? Why?
Dilate because you want as much light as possible to allow for optimal vision
Define refraction and accommodation
Refraction: the bending of light that passes through the cornea and hits the lens (refractive structures of the eye), allows light to focus to produce clear images
Accommodation: adjust thickness of the lens in the eye to ensure refraction is focusing light in retina
In your own words, describe what is happening when an individual is near-sighted (myopia) and when a person is far-sighted (hyperopia).
It has to do with the eyes ability for accommodation.
Near: lens is longer or too spherical or too strong,close clear, far blurry
Far: eye too short, lens too weak/thin, close blurry, far clear
What is the term for the gradual loss of visual acuity that occurs with age?
presbyopia
What are rods and cones? How do their functions differ?
Both convert light into neural impulses. Differ in number, location, function
(more) rods: see at low light levels, black and white (see in shades), lower level of detail
(less) cones: colors, light sensitivity to light, concentrated in retina
Trace the visual pathway from the external environment to the central nervous system.
What does the term “visual field” refer to?
The total are in which objects can be seen in the peripheral vision as you focus your eyes on a central point. Left side of brain is receiving info from the right half od the visual fiend of both eyes
What is the significance of the optic chiasm?
Where nerve fibers from the medial aspect of both optic nerves cross over at optic chiasm and up the optic tract on opposite side
If a person sustains an injury to their left optic tract, how will this impact their vision?
Will lead to same died visual loss/ blindness, info from lwft optic nerve is going to be visual loss to left eye
What areas will they be able to see and in what areas of the visual field will they experience visual loss?
If a person sustains an injury to the optic nerve of their right eye, how will this impact their vision? What areas will they be able to see and in what areas of the visual field will they experience visual loss?
Hearing & Equilibrium
What are the structures of the middle ear? What are their functions? What are the other names for the “auditory tube”?
Tympanic cavity, auditory tube, auditory ossicles} function is to transport airborne sound waves from external ear
What are the structures of the inner ear? What are their functions?
Cochlea: contains receptors that function to convert sound waves into nerve impulses so hearing is possible
Vestibular apparatus: needed for sense of equilibrium/balance
Describe the functions of the auditory tube and explain why ear infections are more common in children than adults.
Ventilation of the middle ear (auditory tube plays a part in equalizing pressure between the outside world and middle ear. Protection. Drainage → drains substances into the nasal fairings to gather with other excretions. Because of the shape of the auditory tube. The angle is different, in kids it is perpendicular. It is a lot easier for fluid and debris to get stuck in eustachian tube
How does sound travel from the external environment to the central nervous system? Explain the structures and steps involved in this pathway.
Sound waves strike tympanic membrane and it vibrates → vibrations are transferred through the middle ear to the ossicles → vibrations move those bones and movement impacts oval window which is the entrance to the cochlea →movement in the bones cause waves in cochlear fluid → causes motion in the basilar membrane, the hair cells on the membrane bend and create neural signal → neural signal travels to auditory complex = sound!
What is the auditory/acoustic reflex?
Example: when you hear something really loud the muscles of the inner ear will stiffen, protective feature, not sustainable though
What are the primary structures of the vestibular apparatus (balance/equilibrium) and how do they inform our sense of balance?
Semicircular canals: directing front to back, side to side, rotational movement of head
Otolith organs: detect linear movement, sensitive to acceleration or deceleration (roller coaster)
What is the difference between conductive and sensorineural hearing loss?
Conductive (sound waves making it to the inner ear) : sound wave/ vibrational movements not making it into the inner ear, blockage or ossicles aren't moving
sensorineural (nerve connection): function of inner ear issues with auditory nerve, inner ear, auditory pathway