Chapter 4: The Nervous System

Question 1

Define neurons.

Answer 1

specialized cells capable of transmitting electrical impulses and then translating those electrical impulses to chemical signals

Question 2

Synaptic bouton

Question 3

Axon hillock

Question 4

Synapse vs synaptic cleft

Question 5

What are nerves?

Answer 5

bundles of neurons in the peripheral nervous system

can be classified as sensory, motor, or mixed (both sensory and motor)

Question 6

What are tracts?

Answer 6

bundles of axons within the central nervous system

only carry one type of information

Question 7

What is a nuclei?

Answer 7

a collection of cell bodies in the CNS

a grouping of the cell bodies of neurons in the same tract

Question 8

What is a ganglion?

Answer 8

a collection of cell bodies in the PNS

Question 9

What are glial cells (neuroglia)?

Answer 9

cells within the nervous system which are not neurons but support and myelinate neurons

play both structural and supportive roles

Question 10

State and describe 5 types of glial cells.

Answer 10

astrocytes: nourish neurons and form the blood-brain barrier

ependymal cells: line the ventricles of the brain and produce cerebrospinal fluid which acts as a shock absorber for the brain

microglia: phagocytic cells that ingest and break down waste products and pathogens in the CNS

oligodenrocytes: produce myelin around axons within the CNS

Schwann cells: produce myelin around axons within the PNS

Question 11

The equilibrium potential of potassium

Question 12

What does the resting membrane potential result from and which value is it?

Answer 12

the net effect of both sodium equilibrium potential (+60mV) and potassium equilibrium potential (-90mV) as these ions flow through sodium and potassium leak channels in an attempt to reach their electrical/chemical equilibrium

approximately -70mV for the average neuron (inside of the neuron is more negative than the exterior)

Question 13

What is the purpose of the sodium/potassium ATPase?

Question 14

Describe inhibitory inputs.

Answer 14

cause hyperpolarization (raise the membrane potential)

make the neuron more likely to fire an action potentials

Question 15

Inhibitory input causes ______.

Answer 15

causes hyperpolarization (lowers the membrane potential)

makes the neuron less likely to fire an action potential

Question 16

What is the threshold voltage to trigger an action potential?

Answer 16

the axon hillock must receive enough excitatory input to be depolarized to -55 to -40 mV

Question 17

Describe summation.

Answer 17

the additive effect of multiple signals received by a given neuron, both excitatory and inhibitory

Question 18

What are the 2 types of summation.

Answer 18

temporal and spatial

Question 19

Temporal summation

Answer 19

one presynaptic neuron delivers multiple signals during a relatively short time period

Question 20

Spatial summation.

Answer 20

multiple presynaptic neurons deliver signals at the same time

Question 21

Absolute vs relative refractory periods.

Question 22

Impulse propagation.

Question 23

Saltatory conduction.

Question 24

Describe the event of the action potential.

Question 25

What is an effector?

Answer 25

a post-synaptic cell which is a part of a gland or muscle rather than another neuron

Question 26

Describe the events at the synapse once the action potential reaches the terminus.

Answer 26

* voltage gated calcium channels open and calcium enters the cell * the calcium influx triggers fusion of the membrane-bound vesicles with the cell membrane at the synapse * the neurotransmitters are released into the synaptic cleft via exocytosis * the neurotransmitters diffuse across the cleft and bind to receptors on the postsynaptic membrane

Question 27

The distinction between excitatory and inhibitor signals is ultimately determined by the \_\_\_\_\_\_\_\_\_\_\_.

Answer 27

postsynaptic neurotransmitter receptors

Question 28

Neurotransmitter receptors tend to be either _______ or \_\_\_\_\_\_\_.

Answer 28

ligand-gated ion channels G protein-coupled receptors

Question 29

Differentiate ligand-gated ion channels and G protein-coupled receptors.

Answer 29

**ligand-gated ion channels:** result in the postsynaptic cell being either depolarized or hyperpolarized **G protein-coupled receptors:** results in changes in cAMP levels or a calcium influx within the postsynaptic cell

Question 30

Describe the 3 main mechanisms by which neurotransmitters are removed from the synaptic cleft.

Answer 30

* neurotransmitters can be broken down by **enzymes** (acetylcholine) * neurotransmitters can be brought back into the presynaptic neuron via **reuptake** carriers (ex. serotonin, dopamine, norepinephrine) * neurotransmitters can **diffuse** out of the synaptic cleft (ex. nitric oxide)

Question 31

List and describe the 3 general kinds of nerve cells in the nervous system.

Answer 31

**sensory neurons (afferent neurons):** transit sensory information from receptors to the spinal cord an brain **motor neurons (efferent neurons):** transmit motor information from the brain and spinal cord to the muscles and glands **interneurons:** found between other neurons; most numerous; located predominantly in the brain and spinal cord and are often linked to reflexive behaviour

Question 32

Supraspinal circuits.

Question 33

Describe the major divisions of the human nervous system.

Answer 33

Question 34

Name and describe the 2 types of matter found in the brain.

Answer 34

**white matter:** consists of _axons_ encased in myelin sheaths **grey matter:** consists of unmyelinated _cell bodies_ and _dendrites_ *note: in the brain, white matter lies deeper than grey matter; in the spinal cord, grey matter lies deeper than white matter*

Question 35

Differentiate somatic and autonomic nervous systems.

Answer 35

the 2 divisions of the PNS somatic = voluntary autonomic = automatic

Question 36

Describe the somatic nervous system.

Answer 36

consists of sensory an motor neurons sensory neurons transmit information thought afferent fibres motor neurons transmit information thought efferent fibres

Question 37

Describe the autonomic nervous system.

Answer 37

manages the **involuntary** muscles associated with many internal organs and glands (independent of conscious control) ex. regulates heartbeat, respiration, digestion, glandular sections, temperature control

Question 38

What are the 2 divisions of the autonomic nervous system?

Answer 38

parasympathetic: rest and digest sympathetic: fight or flight

Question 39

What are the 4 divisions of the spinal cord?

Answer 39

cervical thoracic lumbar sacral

Question 40

Describe the structure of the spinal cord.

Answer 40

contains the axons of motor and sensory neurons sensory neurons: * bring information in from the periphery * enter on the dorsal (back) side of the spinal cord * cell bodies are found in the dorsal root ganglia motor neurons * exit the spinal cord ventrally (front side)

Question 41

What is a key difference between the somatic and autonomic nervous systems.

Answer 41

_somatic nervous system:_ motor neuron goes directly from spinal cord to muscle **(1 neuron)** autonomic nervous system: a preganglionic neuron with its soma in the CNS travels to a postganglionic neuron in the PNS which then affects the target tissue **(2 neurons)**

Question 42

Describe the parasympathetic nervous system.

Answer 42

main goal is to conserve energy (rest and digest) associated with resting and sleeping states reduces heart rate and constricts bronchi controlled by acetylcholine vagus nerve

Question 43

Describe the sympathetic nervous system

Answer 43

* increases heart rate * redistributes blood to muscles of locomotion * increases blood glucose concentration * relaxes bronchi * decreases digestion and peristalsis * dilates the eyes to maximize light intake * releases epinephrine into the bloodstream

Question 44

What are reflex arcs? (2)

Answer 44

* the nerve pathway involved in a reflex reaction * use the ability of interneurons in the spinal cord to relay information to the source of a stimulus while simultaneously routing it to the brain

Question 45

What are the 2 types of reflex arcs?

Answer 45

monosynaptic and polysynaptic

Question 46

Explain monosynaptic reflex arcs and provide an example.

Answer 46

explanation * there is a single synapse between the sensory neuron that receives the stimulus and the motor neuron that responds to it example: knee-jerk reflex * when the patellar tendon is stretched, information travels up the sensory neuron to the spinal cord where it interfaces with the motor neuron that contracts the quadricep muscles

Question 47

Explain polysynaptic reflex arcs.

Answer 47

explain: * the sensory neuron may fire directly onto a motor neuron as well as interneurons that fire onto other motor neurons example: the withdrawal reflex; stepping on a nail * stepping on a nail will send sensory signals to pul the foot away from the nail * however, the muscles in the other leg must be stimulated to account for the lifted food and maintain balance * interneurons in the spinal cord connect the incoming sensory information to the motor neurons in the supporting limb