Human Physiology Exam 3

CNS contains

Brain and Spinal Cord

PNS (Peripheral Nervous System) contains

Afferent Pathways, Efferent Pathways, Sympathetic Division, Parasympathetic Division, and Somatic Nervous System

Autonomic Nervous System

Sympathetic Division and Parasympathetic Division

Afferent Pathways

go toward CNS

Efferent Pathways

send information from CNS

Sympathetic Division

excitatory division

Parasympathetic Division

inhibitory divison

Somatic (Motor) Nervous System

stimulates skeletal muscle contraction

Afferent Neurons

originate in the periphery of the body via a sensory or visceral receptor and travel toward CNS

Efferent Neurons

originate in CNS and travel to periphery to produce an effect in the body

Interneurons

found in CNS; allow communication between afferent and efferent neurons

Excitable Cells

cells that can produce electrical signals

Action Potential

electrical signals produced by excitable cells

Neurons (nerve cells)

excitable cells in nervous system

Glial Cells

structural cells found in nervous system (90% of cells in NS)

Cell Body

contains nucleus

Dendrites

receives information from other neurons or stimuli

Axon

sends impulse (action potential) away from cell body

Axon Terminal

releases neurotransmitter

Myelination

due Schwann cells wrapping around axons creates myelin sheath that acts as “insulation”. Increases conviction velocity of nerve impulse

Membrane Potential

created in excitable cells (e.g. neurons) by separating oppositely charged ions

Inside of the Excitable Cell

has a negative charge relative to the outside. Thus, the resting membrane potential of a neuron is a negative value (-70mV)

Depolarization

when an excitable cell’s membrane permeability is altered, the membrane potential changes

Action Potential

depolarization spreads along the cell membrane which allows electrical signals to be transmitted in neuron. “Spread of depolarization”

Where are Gated Ion Channels found

dendrites, cell body, and axon hillock region of a neuron

What do Gated Ion Channels create

graded potentials following activation by voltage changes, ligand/receptor interactions, or mechanical stimulation

Voltage Gated Channels

open with change in voltage (in axon hillock)

Ligand Gated Channels

open due to binding of ligand to membrane receptor (in dendrite)

Mechanically Gated Channels

open due to mechanical stimuli (on dendrite or cell body)

Graded Potentials

small changes in membrane potential due to ion channels opening (or closing) following stimulation by another source

What do Graded Potentials create

action potential if they cage membrane potential above threshold level; if depolarization occurs these are called excitatory graded potentials

Hyperpolarization (make membrane potential more negative)—>

inhibitory graded potentials

Action Potential Phases

depolarization, depolarization, after-hyperpolarization

Action Potentials in Unmyelinated Axons

• An action potential “propagates” down an

axon based on electrochemical gradients

• Positive charges move from the area that has

been depolarized to the adjacent area on the

membrane. This depolarizes that area.

• Current flows to adjacent areas based on

electronic conduction

• Larger diameter axons have faster

conduction velocities (less resistance to

current flow down axon)

Action Potentials in Myelinated Axons

• Saltatory (“to leap”) conduction is used to

propagate action potentials in axons with

myelin sheaths.

• Action potentials cannot be produced in

areas where myelin is present, so the

current flows from node to node very

quickly

• Fastest conduction velocities are found in

large diameter myelinated axons

Synaptic Transmission

• Action potential reaching axon terminal

stimulates vesicular movement to terminal

membrane by opening calcium channels;

vesicles release neurotransmitter into synaptic

cleft

• Neurotransmitter diffuses to postsynaptic

membrane and binds to receptors to initiate a

postsynaptic cell response

• Neurotransmitter is degraded by enzyme on

postsynaptic cell membrane or taken back up

into presynaptic cell

• Synapses can be either excitatory or inhibitory

Excitatory Synapses

these bring postsynaptic neurons closer to threshold for AP to occur, depolarization is called an excitatory postsynaptic potential (EPSP)

Fast Excitatory Response

NT opens ion channels allowing for a rapid depolarization

Slow Excitatory Response

NT activates a G-protein/2nd messenger cascade that is slower to create a depolarization of the membrane

Inhibitory Synapses

causes postsynaptic neuron membrane potentials to be hyper polarized or stabilized so a depolarization is less likely to occur. one type is called an inhibitory post-synaptic potential (IPSP)

Convergence

when a number of presynaptic neurons synapse one one postsynaptic neuron

Temporal Summation

when two or more postsynaptic potentials are produced in rapid succession at the same synapse and are additive to create a greater depolarization (or hyperpolarization)

Spatial Summation

when two or more postsynaptic potentials from different synapses overlap and are additive

Modulatory Synapses

regulate communication across another synapse

Axoxaxonic Synapses

form between axon terminals of two different neurons; these are modulatory synapses

Presynaptic facilitation can occur:

this increases the release of NT from the postsynaptic neuron

Presynaptic inhibition can occur:

this decreases the release of NT from postsynaptic neuron

Is myelin present and example of function for A alpha

yes

stimulation of skeletal muscle contraction

Is myelin present and example of function for A beta

yes

touch, pressure sensation

Is myelin present and example of function for A gamma

yes

stimulation of muscle spindle contractile fibers

Is myelin present and example of function for A delta

yes, but a little

pain, temperature sensationIs myelin present and example of function for

Is myelin present and example of function for B

yes

visceral afferents, autonomic preganglionics

Is myelin present and example of function for C

no

pain, temperature sensation, autonomic postganglionics

NTs:

transmit signal from one neuron to another neuron or target cell

must bind to specific receptor on postsynaptic cell membrane

Acetylcholine

released from neurons in both CNS and PNS

produced from acetyl coA and choline by the enzyme choline acetyl transferase (CAT)

binds to cholinergic receptors

Cholinergic Receptor Types

Nicotinic Cholinergic Receptors and Muscarinic Cholinergic Receptors

named this way because nicotine can bind to the first class and muscarine to the second

the effect on the postsynaptic cells differs depending on the receptor Ach binds to

Nicotinic Cholinergic Receptors

Ach binding to nicotinic receptors causes opening of sodium and potassium channels (ionotropic) causing an EPSP

These receptors are found in the peripheral nervous system (on muscle cells and autonomic neurons)

Muscarinic Cholinergic Receptors

• The receptors are metabotropic (work via a second messenger system in postsynaptic cell)

• These receptors are the main receptor type in the CNS and are also found on some effector organs in the body

Biogenic Amines

derived from Catecholamines, Serotonin, and Histamine

Catecholamines

EPI, NE, and dopamine

receptors for EPI and NE are called adrenergic receptors (alpha and beta) with subtypes of each

EPI has high affinity for

beta2

Norepinephrine has a high affinity for

alpha and beta1

Receptors for dopamine are called

dopaminergic

Serotonin (5-hydroxytryptamine; 5-HT)

found in GI tract and CNS

receptors are called 5-HT receptors with numerous subtypes

Histamine

found in CNS as a NT

receptors are called histamine receptors with numerous subtypes

Where does degradation and reuptake of biogenic amines occur

synapses

Enzyme that degrades biogenic amines (EPI, NE, 5-HT); this enzyme is inhibited how?

Monoamine Oxidase

inhibited by MAO-A

Reuptake Molecule - reuptake inhibited how?

SSRIs

Neuropeptides

short chains of amino acids found in neurons and function as neurotransmitters. Many are also hormones (e.g., TRH, ADH, oxytocin, substance P, endogenous opioids, orexin)

Purines example

ATP, adenosine

Chemical substances that function as NTs

Nitric Oxide

Endocannabinoids: released during exercise

CNS Physiology

• Composed of the brain and spinal cord

• Bathed inside and out by cerebrospinal fluid (CSF) that has a similar composition to plasma

• CSF is the interstitial fluid of the CNS

• Receives 15% of blood pumped by the heart (due to high metabolism)

• Brain consumes 20% of the body’s

  oxygen intake and 50% of the body’s

  glucose intake (the brain relies on

  glucose for energy)

Interruption in blood flow to CNS can cause irreversible damage: why?

glycogen is not stored in CNS, fatty acids re not available to CNS, CNS cannot produce energy anaerobically

Blood-Brain Barrier

• Protects the CNS from harmful substances

• Small molecules, gases and lipophilic

molecules are able to penetrate it from the

blood

• Large molecules and lipophbic molecules

cannot pass through unless they have

transport proteins

• Tight junctions restrict transport between

endothelial cells of brain capillaries

• The fluid on the brain side of the barrier is

cerebrospinal fluid (CSF)

Brain consists of three main parts

Forebrain, cerebellum, and brainstem

Forebrain

right/left hemispheres; consists of cerebrum and diencephalon

Cerebrum

contains cerebral cortex (surface) and subcortical nuclei (deeper)

Cerebral Cortex

carries out highest level of neural processing; perceptions, ideas, memory, motor control all originate here; integrating center that receives and processes sensory information to formulate thoughts and actions

Diencephalon

contains thalamus and hypothalamus

Thalamus

filters and refines sensory information before it reaches the cerebral cortex; also involved in motor movement control

Hypothalamus

releases tropic hormones to anterior pituitary and controls posterior pituitary hormone release; produces hunger and thirst and is also involved in emotions; regulates body temperature (thermostat)

Cerebellum

inferior to forebrain and posterior to brainstem

functions in motor coordination and balance and provides feedback to produce smooth motor movements

Brainstem

connects cerebrum and cerebellum to spinal cord

3 regions: midbrain, pons, and medulla oblongata

• Brainstem areas process cranial nerve

information

• Brainstem controls sleep-wake cycles,

consciousness, and arousal of the cerebral

cortex via the reticular formation

• Brainstem contains areas that regulate

autonomic functions such as the

cardiovascular and respiratory control

Limbic System

collection of areas that function in learning and emotions; controls “basic drives”

Areas include:

• amygdala

• hippocampus

• fornix

• cingulate gyrus

• hypothalamus

• thalamus

Voluntary Motor Control 4 Processes

• the idea of intention to move

• development of a program of motor commands

• execution of the program of motor commands

• continual feedback to assess and refine the movement

Emotions

involve many areas of the brain

produced by either sensory input or memories

responses to such stimuli result in autonomic, motor, and hormonal changes

Sensory Physiology

Stimuli from both the internal and external environments are detected by sensory receptors

External Stimuli are detected by the

1. somatosensory system – for skin sensations

2. proprioceptors – for detecting limb position/motion

3. special sensory systems – for vision, smell, taste, hearing, balance and equilibrium

• Internal stimuli are detected by visceral receptors that transmit signals to the CNS via visceral afferents

• Sensory receptors detect different stimuli based on the stimulus modality (i.e., temperature, pressure, light/sound waves, etc.)

Somatosensory System

receptors in this brand of the nervous system respond to pressure, pain, temperature, and body position

Mechanoreceptors and Thermoreceptors in Somatosensory System

mechanoreceptors respond to pressure, force and vibration; thermoreceptors respond to temperature; nociceptors respond to injurious stimuli (pain)

Perception of Pain

Pain allows an individual to recognize injurious stimuli and to avoid future encounters with such stimuli

Nociceptors

allows for pain perception along with autonomic emotional and reflex responses

Pain types

fast and slow

fast: the sharp, pricking, well-localized type

slow: slow is the dull, aching, poorly0localized type

Visceral Pain

detected by nociceptors that are stimulated by tissue- damage in internal structures

Referred Pain

normally the result of visceral pain; it occurs due to second-order neurons receiving signals from somatic afferents along with the visceral afferent; the brain can perceive the pain as coming from elsewhere due to this

Pain Modulation

pain signals can be facilitated or inhibited as they travel along sensory pathways; this can occur wherever there is a synapse

Gate-Control Theory of Pain

inhibitory interneurons in spinal cord stimulated by skin mechanoreceptors can inhibit the second-order neurons in the spinal cord that transmit pain information

Endogenous Analgesia System

the MT enkephalin is released from inhibitory interneurons to inhibit synaptic transmission from the nociceptive afferent to the second-rider neuron

Autonomic and Somatic (Motor) Nervous Systems

both autonomic and somatic nervous systems are efferent pathways

Autonomic

innervates all effector organs except skeletal muscle and function to maintain homeostasis

divisions: sympathetic (fight or flight) and parasympathetic (resting)