Exam 7: Nervous System

1. collect sensory information

2. process and evaluate sensory information

3. initiate a motor response to stimuli

What are the three main functions of the nervous system?

1. anterograde

   1. moves vesicles, organelles, and glycoproteins AWAY FROM the cell body via the axon or synaptic knobs

2. retrograde

   1. moves enzymes or new axoplasm TO the cell body from the axon or synaptic knobs

What are the two types of transport in neurons?

initiate action potentials, house organelles, integrate information, and maintaining neuron structure

What is the function of the cell body?

to receive input from other neurons and transfer it to the cell body

What is the function of the dendrites?

to conduct action potentials and release neurotransmitters at synaptic knobs

What is the function of the axon?

1. astrocytes

   1. forms the blood-brain barrier (controls which substances have access to the brain), regulates ion levels, and is supportive

2. ependymal cells

   1. lines cavities in brain and spinal cord

3. microglia

   1. wanders the CNS and replicates during infection (phagocytic cells)

4. oligodendrocytes

   1. myelinates and insulates CNS axons

What are the 4 types of glial cells exclusive to the CNS?

1. satellite cells

   1. electrically insulates and regulates the exchange of nutrients and waste

2. Schwann cells (neurolemmocytes)

   1. flat, long cells that wrap PNS axons with myelin to allow faster action potential propagation

What are the 2 types of glial cells exclusive to the PNS?

1. multipolar

   1. many dendrites, and one axon

2. bipolar

   1. one dendrite, and one axon

3. unipolar

   1. contains one process that extends from cell body

What are the 3 shapes of neurons?

1. sensory neurons

   1. conducts input from somatic and visceral effectors

2. motor neurons

   1. conducts output from CNS to somatic and visceral effectors

3. interneurons

   1. communicates between sensory and motor neurons (found in spinal cord and brain)

What are the 3 types of functional neurons?

presynaptic neurons produce signals (by the release of neurotransmitters)

postsynaptic neurons receive signals (by binding neurotransmitters)

What are presynaptic neurons and postsynaptic neurons?

to insulate the axon for faster propagation of action potentials

What is the purpose of myelin sheaths?

a pump is a membrane protein that maintains a concentration gradient by moving substances against their concentration gradient (requires cellular energy)

a channel is a membrane protein that allows ions to move with their concentration gradients into or out of a cell

What is the difference between a pump and a channel in neuron membranes?

1. leak (passive)

   1. always open for continuous diffusion of ions

2. chemically gated

   1. opens when neurotransmitters bind to them

3. voltage gated

   1. opens when the charge of the membrane changes

4. modality gated

   1. opens in response to specific types of sensory stimuli, such as change in temp or pressure

What are the 4 types of channels?

-70 mV

caused by the greater concentration of potassium inside the cell, and sodium outside

inside is more negative, outside is more positive

What is the typical resting membrane potential of neurons and what causes it?

to establish and maintain the resting membrane potential

sodium and potassium move against their concentration gradient to keep RMP

What is the function of sodium potassium pumps?

a change in membrane potential in the negative direction

this happens after repolarization when potassium channels remain open for an extended time allowing more K⁺ to leave the cell

• this results in a more negative membrane potential than normal RMP

• action potentials CANNOT fire during hyperpolarization

What is hyperpolarization and what causes it?

relatively small, short-lived changes in the resting membrane potential that are caused by the movement of small amounts of ions across the plasma membrane

they are localized

can result in positive or negative changes in charge (relative to RMP)

What are local (graded) potentials?

potentials in the postsynaptic neuron that result in the neuron becoming more positive

1. neurotransmitters enter the cleft and bind to chemically gated channels

2. channels open and allow Na⁺ to flow in and a little bit of K⁺ to flow out

3. when enough Na⁺ comes into the cell, EPSP results

4. EPSP moves toward the initial segment of the neuron (axon hillock area), but gets weaker

What are excitatory postsynaptic potentials (EPSPs) and how are they generated?

potentials in the postsynaptic neuron that result in the neuron becoming more negative

this happens to reduce the likelihood of action potentials firing (during hyperpolarization)

1. neurotransmitter is released into the cleft and binds to chemically gated K⁺ or Cl^- channels

2. channels open and K⁺ flows out of cell causing the cell to become more negative (when K⁺ channels are present) or Cl^- moves into the neuron causing a negative charge inside (when Cl^- channels are present)

3. the inflow of Cl- or outflow of K+ initiates an IPSP

4. IPSP moves towards the initial segment of the neuron (axon hillock) but gets weaker as it travels

What are inhibitory postsynaptic potentials (IPSPs) and how are they generated?

when multiple locations in the receptive regions of the neuron (cell body & dendrites) receives neurotransmitters simultaneously and generates PSPs

What is spatial summation?

one presynaptic neuron repeatedly releases neurotransmitters and produces multiple EPSPs in a short period of time

What is temporal summation?

1. Na⁺ enters the axolemma and triggers Na⁺ voltage-gated channels in adjacent regions to open as well

2. Na⁺ entering the axon causes the membrane to have a positive charge

   1. channels then enter an inactivation state (close)

   2. steps 1 and 2 repeat as the impulse moves toward the synaptic knob

3. depolarization slowly opens K⁺ channels and K⁺ flows out, causing negative membrane potential

4. K⁺ channels stay open for a longer time, so K⁺ exit makes the cell more negative than RMP (hyperpolarization)

5. K⁺ channels eventually close and RMP is established

   1. steps 3-5 repeat as the signal reaches the synaptic knob

List the 5 steps of an action potential

a period of time after the start of an action potential when it is impossible or difficult to fire another action potential

What is a refractory period?

absolute refractory period

• when absolutely no stimulus can initiate an action potential

• happens during depolarization and most of repolarization

relative refractory period

• another action potential is possible, but the minimum stimulus strength is now greater

• happens after absolute, during hyperpolarization

What is the difference between the absolute and relative refractory periods, and when do they occur during the action potential?

the sequential opening of Na⁺ and K⁺ channels along the entire length of an axon to the synaptic knob

occurs in unmyelinated axons

What is continuous conduction?

occurs when an action potential is only generated on the neurofibril nodes of an axon

happens on myelinated axons

fast and requires less ATP

Steps:

1. action potential occurs at a node

2. Na+ diffuses into axolemma in the myelinated region of the axon and creates a weak current

   1. happens very fast

3. weak current arrives at the next node and triggers another action potential

   1. signal “jumps” from node to node

   2. AP travels down the axon to the synaptic knob

What is saltatory conduction?

1. acetylcholine

2. biogenic amines

   1. neurotransmitters created from slightly modified amino acids

3. amino acids

   1. examples include glutamate, glycine, and GABA

4. neuropeptides

   1. chains of amino acids

   2. example: endorphins

What are the 4 classes of neurotransmitters? Give an example of each

1. catecholamines

   1. made from tyrosine

   2. examples include dopamine and norepinephrine

2. indoleamines

   1. made from histidine or tryptophan

   2. example: serotonin

What are the two types of biogenic amines?

primary neurotransmitter in NMJ and in most of the ANS

What is the function of acetylcholine?

produces inhibitory activity in the brain

plays a role in cognition, motivation, behavior, and mood

What is the function of dopamine (NTM)?

found in sympathetic division of the ANS

increases alertness, attention, and arousal

What is the function of norepinephrine (NTM)?

has various effects in the thalamus, hypothalamus, and spinal cord

What is the function of epinephrine (NTM)?

CNS neurotransmitter, plays a role in sleep and memory

What is the function of histamine (NTM)?

various functions related to sleep, appetite, cognition, and mood

What is the function of serotonin (NTM)?

promotes cognitive function in the brain

What is the function of glutamate (NTM)?

excites activity in descending motor pathways through the spinal cord

What is the function of aspartate (NTM)?

activates diverse areas of the brain

What is the function of serine (NTM)?

primary inhibitory neurotransmitter in brain

influences muscle tone, alcohol, and drugs

What is the function of gamma-aminobutyric acid (GABA)?

inhibits activity between neurons in the brain, spinal cord, and eye

What is the function of glycine (NTM)?

helps regulate response to anything that is perceived to be potentially painful

What is the function of enkephalin (NTM)?

prevents release of pain signals from neurons and fosters a feeling of wellbeing

What is the function of beta-endorphin (NTM)?

memory regulation and mood balance

What is the function of neuropeptide Y (NTM)?

inhibits activity of some neurons

What is the function of somatostatin (NTM)?

assists with pain transmission to the brain

What is the function of substance P (NTM)?

stimulates neurons in the brain to mediate fullness and repress hunger

What is the function of cholecystokinin (NTM)?

helps control effects of dopamine

What is the function of neurotensin (NTM)?

has an inhibitory effect on neurons in brain and spinal cord

What is the function of adenosine (NTM)?

involved in learning and memory and relaxation of muscle in GI tract

What is the function of nitric oxide (NTM)?

chemicals (other than neurotransmitters) that alter the responses of local neurons

1. facilitation

   1. causes an increased response in the postsynaptic neuron

   2. may increase the amount of neurotransmitters in the cleft or number of receptors on the postsynaptic neuron

2. inhibition

   1. causes weaker responses in the postsynaptic neuron

   2. may decrease the amount of neurotransmitters in the cleft or number of receptors on the postsynaptic neuron

What are neuromodulators and what are the two types of responses they produce?

nitric oxide

• believed to strengthen memory in the CNS and cause vasodilation in the PNS

endocannabinoids

• decreases neurotransmitter release from presynaptic neurons

• alters learning, memory, and appetite

What are the functions of the two neuromodulators nitric oxide and endocannabinoids?

in the meninges and glial cells

Where do brain tumors typically originate in the CNS?

the progressive demyelination of neurons in the CNS

it is an autoimmune disorder: oligodendrocytes are attacked

can cause scarring and permanent loss of function

What is multiple sclerosis?

disorder characterized by the loss of myelin from peripheral nerves due to inflammation

results in muscle weakness in the limbs

What is Guillain-Barre Syndrome?

the neuron cell body is intact and enough neurolemma remains

also success is more likely if the damage is less extensive

PNS axon regeneration after injury is possible if-

1. enzymes degrade the NTs (happens with ACh)

2. presynaptic neuron reuptakes the NT

3. NT may diffuse away from the synapse and get absorbed by neuroglia

What are the three ways neurotransmitters can be removed from the synaptic cleft?

composed of a presynaptic neuron and a postsynaptic neuron

presynaptic neuron produces a signal (such as ACh) and the postsynaptic neuron receives the signal

What is the structure and function of a typical chemical synapse?

composed of a presynaptic neuron and postsynaptic neuron physically bound together

gap junctions are found in the plasma membranes of both neurons

sends fast signals and is less common in humans

What are electrical synapses?

• excitatory cholinergic synapse

  • ACh is released by the presynaptic neuron, triggering an EPSP, think acetylCHOLINE

• excitatory adrenergic synapse

  • norepinephrine is released by presynaptic neuron, triggering an EPSP, think ADRENaline

• inhibitory (GABA-erginic) synapse

  • neurotransmitters released by the presynaptic neuron causes the postsynaptic neuron to initiate an IPSP

What is the difference between:

• an excitatory cholinergic synapse

• an excitatory adrenergic synapse

• and an inhibitory (GABA-erginic) synapse?

• processes are regulated unconsciously

• transmits signals from CNS to the heart, smooth muscle, and glands

• responds to visceral sensory inputs

• functions to maintain homeostasis

What are four general qualities of the autonomic nervous system?

Parasympathetic division

• conserves bodily energy and maintains homeostasis

• activity is fairly localized (only influences a few effectors at once)

Sympathetic division

• kicks in during exercise or emergency

• activates many effectors at a time (mass activation)

How is the parasympathetic and sympathetic divisions of the ANS different?

the process of the parasympathetic and sympathetic divisions of the ANS both continuously releasing neurotransmitters to regulate the activity of effectors

this allows an effector to be controlled by the change IN TONE by one of the two divisions

What is autonomic tone?

also called autonomic reflexes, pre-programmed responses to stimuli generated by a reflex arc

Arc:

• receptor

• sensory relay to CNS

• CNS integration center

• motor neuron

• effector

What are visceral reflexes and what does the visceral reflex arc consist of?

reduction of blood pressure:

1. when BP elevates, receptors in the walls of large vessels are stimulated

2. nerve signals are propagated to the cardiac center in the medulla

3. parasympathetic output is relayed along motor neurons that innervate the heart

4. BP decreases

Give the steps of blood pressure reflex (visceral reflex)

• oculomotor nerve

• facial nerve

• glossopharyngeal nerve

• vagus nerve

additionally, some neurons that stem from S2-S4 of the spinal cord are also a part of the parasympathetic division

What four cranial nerves are a part of the parasympathetic division of the ANS?

condition caused by injury to the cervical or T1 sympathetic ganglion, can cause the following symptoms:

• ptosis

  • drooping of eyelid due to paralysis

• miosis

  • constricted pupil due to paralysis

• anhydrosis

  • lack of sweating bc sweat glands lack innervation

• facial flushing

What is Horner Syndrome?

it binds to β2 receptors on the bronchioles in the lungs

this relaxes the smooth muscles of bronchioles

How does epinephrine treat asthma?

condition caused by the sudden constriction of small arteries in the digits which results in loss of skin hue

due to exaggerated local sympathetic response

triggered by coldness or emotional stress

What is Raynaud Syndrome?

• tropicamide

  • blocks muscarinic receptors, causes pupil dilation

• illicit drugs

  • cocaine, amphetamines, LSD, and PCP also dilate pupils

What two drugs affect pupil size?

vascular condition that causes BP to rise profoundly

stimulates a sympathetic reflex- causes vasoconstriction and large increase in BP

caused by hyperactivity of ANS after a spinal cord injury

What is autonomic dysreflexia?

to stimulate the release of epinephrine and norepinephrine into the bloodstream to initiate the ‘fight or flight’ response

What is the role of the adrenal medulla in the sympathetic nervous system?

autonomic motor pathways regulate involuntary controls, such as heart rate and digestion

somatic motor pathways regulate voluntary controls, such as skeletal muscle movement

How are autonomic motor pathways different from somatic motor pathways?

rapid, preprogrammed, and involuntary responses of muscles or glands to a stimulus

What are reflexes?

the neural pathway responsible for generating a response to a stimulus

• receptor

• sensory neuron

• integration center

• motor neuron

• effector

What is a reflex arc?

long, short

*ganglia are close to or within the effector

In the parasympathetic ANS, the preganglionic axons are ___ and the postganglionic axons are ___

short, long

*ganglia are close to the spinal cord

In the sympathetic ANS, the preganglionic axons are ___ and the postganglionic axons are ___