Anatomy and Physiology - Nervous System

What makes up the central nervous system?

brain, spinal cord

What makes up the peripheral nervous system?

cranial nerves, spinal nerves

What makes up the somatic nervous system and is it voluntary or involuntary?

voluntary

made of skeletal muscles

What makes up the autonomic nervous system? Is it voluntary or involuntary?

• Is the motor subdivision of the PNS

• Involuntary

• Regulates heart, viscera and glands

• 2 branches: sympathetic and parasympathetic

• 2 motor neurons

  • preganglionic and postganglionic

  • Synapse in a ganglia in PNS

• fight or flight - sympathetic effects

• rest and digest - parasympathetic

Neuroglia

supporting cells or glial cells

Do not transmit impulses

Are mitotic

Microglia

Phagocytes

Oligodendrocytes

Form myelin sheath in CNS

Ependymal cells

• Are ciliated.  Line cavities of the brain and spinal cord to circulate Cerebrospinal Fluid (CSF)

• circulation of CSF

Astrocytes

• make up ½ of all nervous tissue

  • “bouncers” of the CNS – regulate movement of substances out of brain capillaries into neurons

Schwann Cells

Form myelin sheath in PNS

Satellite Cells

Similar functions as astrocytes in CNS

Neurons

~100 billion, amitotic, transmit electrochemical messages 

what are neurons functionally classified as?

• Afferent neurons: sensory

• Efferent neurons: motor

• Interneurons (association neurons): in the CNS - between a sensory and a motor neuron

Cell body

soma

axon

conduct outgoing info

myelin sheath

increases speed of action potential transmission down axon

Nodes of Ranvier

spaces of “naked” axon between myelin

Dendrites

receive incoming info

What is the terminology for groups of neurons in the CNS

Nucleus (nuclei), tract

what is a nucleus (nuclei) and where is it found?

a cluster of neuron cell bodies in the central nervous system

what is a tract and where is it found?

a bundle of axons in the central nervous system

What is the terminology for groups of neurons in the PNS

ganglion (ganglia), nerve

what is a ganglion (ganglia) and where is it found?

a cluster of neuron cell bodies in the PNS

what is a nerve and where is it found?

a bundle of axons in the PNS

reflex

a rapid, predictable, involuntary response to a stimulus

refex arc

neural pathway over which a reflex occurs

components of a reflex arc

sensory receptor, afferent neuron, interneuron, efferent neuron, effector (muscle or gland)

autonomic reflexes

stimulate smooth muscle, cardiac muscle or glands (ex. Emptying bladder and rectum)

somatic reflexes

stimulate skeletal muscle (ex. Patellar knee jerk)

Meninges

connective tissue membranes covering CNS

Dura mater

Outermost, double-layered (one layer adheres to inside of skull), tough/leathery

arachnoid membrane

Middle layer, webby, has villi that return CSF to blood

pia mater

Innermost, clings to gyri and sulci

what is cerebrospinal fluid formed by?

Formed by choroid plexuses

cerebrospinal fluid functions

• Is a watery cushion for the brain and spinal cord

• Gives buoyancy to the brain so pressure at the base of the brain is reduced. 

• As CSF flows to the blood via the arachnoid villi, it takes potentially harmful substances away from the brain. 

• transports hormones to areas of the brain

membrane potential of a neuron

a difference between the net charge inside and outside the cell

resting membrane potential

-70mV in avg neuron

• Inside is more negative than outside b/c there are fewer + ions inside

  • K+ is the primary ion inside

  • Na+ is the primary ion outside

depolarization

• Stimulated neurons depolarize (membrane potential becomes more +)

  • Na+ gates open and Na+ enters cell

    • Think….WHY does the Na+ enter?

  • Inside rapidly becomes positively charged (+35mV)

repolarization

• Membrane potential becomes more – again

  • K+ channels open and K+ exits the cell

  • Inside hyperpolarizes to -75mV but quickly returns to -70mV (resting membrane potential)

action potential

• If the neuron membrane depolarizes to threshold then an Action Potential is generated.

  • Is a rapid change in membrane potential that communicates information

  • Is an all or none event of fixed amplitude that travels in one direction

Na+ channels (open)

• During depolarization

• Channel-blocking and channel-inactivating segments open

Na+ channels (Closed and locked - inactivated)

• During repolarization

• Channel-blocking and channel-inactivating segments closed

Na+ channels (Closed and unlocked)

• When neuron is at rest

• Channel-blocking segment closed but channel-inactivating segment open

absolute refractory period

• The cell membrane cannot immediately produce a second AP because the majority of voltage-gated Na⁺ channels are open and/or inactivated 

  • no amount of depolarizing current can cause another action potential

gyrus (gyri)

elevated ridges

sulcus (sulci)

• shallow grooves

  • Ex. Central sulcus separates frontal and parietal lobes

fissure

• a deep sulcus

  • Ex. longitudinal fissure separates left and right cerebral hemispheres

corpus callosum

fiber tract allowing communication between left and right cerebral hemispheres

what structures make up the forebrain

cerebral cortext, basal nuclei, limbic system (amygdala, hippocampus, cingulate (gyrus) cortex), diencephalon (hypothalamus, thalamus, epithalamus)

what structures make up the epithalamus

pineal gland, choroid plexus

Cerebral cortex

regulates perception, planning, and other mental activities – 80% of brain mass

basal nuclei

play role in control of movement (includes striatum, caudate nucleus, putamen, globus pallidus)

the limbic system (parts too)

Part of the brain that regulates emotions and motivations, especially those related to survival, such as fear, anger, pleasure (from eating, sex, nurturing).  

amygdala, hippocampus, cingulate (gyrus) cortex

how does the limbic system work

Generates responses to situations by using:

• Memories

• Information about how your body is working at that moment

• Current sensory input

Example:  A dog runs and jumps up on you.  Your response can vary depending on the 3 factors listed above.

amygdala

involved in emotional response and memory

hippocampus

involved in memory/learning – sends memories out for long-term storage 

Cingulate (gyrus)cortex

plays a role in expression our emotions through gestures

parts of the diencephalon

hypothalamus, thalamus, epithalamus (pineal gland, choroid plexus of 3rd ventricle)

hypothalamus

Regulation of temp, H2O balance, blood pressure. Controls drives (hunger, thirst, sex, rage), controls production of some hormones (interacts with pituitary gland)

thalamus

gateway for all sensory impulses (except smell) passing up to the cerebral cortex for interpretation. Crude recognition of pleasant vs. pain

epithalamus

pineal gland, choroid plexus of 3rd ventricle

pineal gland

makes melatonin

choroid plexus of 3rd ventricle

makes CSF

brain stem parts

midbrain (corpora quadrigemina (tectum), superior collicus, inferior collicus), tegementum, hindbrain (pons, medulla, reticular formation)

midbrain parts

corpora quadrigemina (tectum), superior collicus, inferior collicus

superior collicus and inferior collicus roles

superior collicus: reflex center for vision

inferior collicus: reflex center for hearing

tegmentum parts and roles

red nucleus: relay nuclei in some descending motor pathways

substantia nigra: dopamine producing neurons – causes Parkinson’s when they degenerate

hindbrain parts

pons, medulla oblongata

pons

one of 2 respiratory centers, bridge for info between cerebrum and cerebellum

medulla oblongata

controls respiration, rate & force of heart contractions,  vasomotor control of BP, swallowing, vomiting, gagging, sneezing, hiccupping, 

reticular formation

(reticular activating system RAS) – sleep/wake behavior, consciousness, filters out repetitive sensory input (ex. Feeling of shirt on your back)

cerebellum

provides coordination for skeletal muscle activity (timing, precision)

somatic sensory area

located on the postcentral gyrus

crossed pathways; interprets sensory info from sensory receptors

primary visual cortex

receives visual input from the eye

visual association area

interprets visual stimuli

frontal association area (prefrontal cortex)

intellect, cognition, personality, judgement, reason, planning

where is the primary motor area

on the precentral gyrus

brocas area

directs the muscles involved in speaking (“bro-ducing” speech)

Wernicke’s area

in the junction of the temporal, parietal and occipital lobes

Interpreting words we read or hear