Nervous system

Question 1

explain the conduction of a nerve impulse along myelinated fibres

Answer 1

1. depolarisation occurs
2. saltatory conduction at nodes of Ranvier
3. cell membrane becomes permeable to sodium ions
4. needs to reach theshold (-55mV)
5. sodium ions inter the cell
6. membrane becomes positive to outside
7. potassium ions diffuse out
8. hyperpolarisation
9. sodium-potassium pump acts: sodium out and potassium in
10. membrane returns to polarised state
11. action potential triggers depolarsiation in adjacent membrane regions

Question 2

explain the transmission of a nerve impulse across a synapse

Answer 2

1. When action potential reaches the axon terminals it triggers calcium gates, causing calcium to flood into the axon terminal
2. The calcium binds with vesicles containing neurotransmitters and allows them to move to the cell membrane, releasing the neurotransmitter into the synaptic cleft
3. These neurotransmitters diffuse across the synaptic cleft and attach to receptors on the membrane of the next neuron (dendrites/post-synaptic membrane)
4. Results in the initiation of an action potential in the post-synaptic neuron (sodium gates open into the dendrites)

Question 3

how do neurotransmitters go away after transmission across a synapse

Answer 3

Diffusion

Re-uptake (back into the axon terminal to be used again)

Broken down

Question 4

how is the nervous system protected

Answer 4

bone

meninges

cerebrospinal fluid

Question 5

explain how bone protects the nervous system

Answer 5

Cranium protects brain, vertebral column protects spinal cord

Protects from physical injury

Question 6

explain how meninges protects the nervous system

Answer 6

Holds brain and spinal cord in place, carry blood vessels to the brain

Inner layer: dura mater

• tough and fibrous
• sticks closely to cranium/vertebral canal
• anchors CNS to bone

Middle layer: arachnoid mater

• loose mesh of fibres
• connects with inner layer

Outer layer: pia mater is delicate

• contains many blood vessels
• sticks closely to the surface of brain and spinal cord

Question 7

explain how cerebrospinal fluid protects the nervous system

Answer 7

Supports brain, gives it a medium to float in

shock absorber - protects from mechanical injury

Occupies space between meningeal layers

Circulates through 4 cavities in the brain and centre of spinal cord

Clear watery fluid containing cells, glucose, proteins, urea and salts

Formed from blood, circulates through CNS and takes nutrients to neurons and removes wastes and eventually returns to capillaries

Question 8

give examples of neurotransmitters

Answer 8

acetylcholine

adrenaline

dopamine

histamine

Question 9

list other functions of the cerebrospinal fluid

Answer 9

Shock absorber, protects from mechanical injury

Delivers nutrients to cells of CNS

Removes wastes

Regulates concentration of H+ and CO2, which regulates breathing

Maintains fluid to bathe cells of the brain

Transport chemical messengers around CNS

Question 10

what are the 2 parts to the cerebrum

Answer 10

cerebral cortex

basal ganglia

Question 11

describe the structure of the cerebral cortex

Answer 11

outer surface of cerebrum, grey matter - 2-4mm thick

folded - rounded ridges called convolutions, shallow downfolds calls sulci, deep downfolds called fissures

longitudinal fissures separate cerebral cortex into 2 cerebral hemispheres

hemispheres have four lobes: frontal, parietal, temporal, occipital

joining the hemispheres at the base of the longitudinal fissure is the corpus callosum (area of white matter)

Question 12

what is the function of the cerebral cortex

Answer 12

involved in thinking, reasoning, learning, memory, intelligence, sense and responsibility

3 basic functions:
sensory areas: interpret impulses

motor areas: control muscular movement

association areas: intellectual and emotional processing

Question 13

explain the structure of the basal ganglia

Answer 13

grey matter below cerebral cortex

composed of tracts - bundles of nerve fibres

mostly unmyelinated axons

outside of CNS

Question 14

what is the function(s) of the basal ganglia

Answer 14

regulates muscle tone

integrates complex muscles actions in complicated, learned ways (e.g. walking)

Question 15

what is the function of the cerebellum

Answer 15

takes place below conscious

receives information from inner ear and stretch receptors in skeletal cells

controls posture, balance and fine coordination of voluntary muscles

damaged cerebellum - jerky, uncontrolled movement

Question 16

describe the structure of the cerebellum

Answer 16

2 hemispheres

surface is folded into parallel ridges

outer folded part of grey matter

inside is white matter that branches to all parts of the cerebellum

Question 17

list some functions of the hypothalamus

Answer 17

regulates body temperature

regulates autonomic nervous system: heart rate, blood pressure

regulates food and water intake

secretion of hormones

Question 18

what 3 components is the brain stem composed of

Answer 18

medulla oblongata

pons

midbrain

Question 19

what is the role of the medulla oblongata

Answer 19

important role in automatically adjusting body functions

regulates swallowing, sneezing, coughing, vomiting

contains 3 centres:

1. cardiac: rate and force of heartbeat
2. respiratory: rate and depth of breathing
3. vasomotor: diameter of blood vessels

INFLUENCES BY HYPOTHALAMUS AND OTHER HIGHER CENTRES OF THE BRAIN

Question 20

explain the functions of the spinal cord

Answer 20

carry sensory impulses to the brain and motor impulses away from the brain

integrate certain reflexes.

Question 21

list some changes that the autonomic nervous system causes

Answer 21

heart rate

blood pressure

digestion

pupil diameter

Question 22

what is meant by a fight or flight response

Answer 22

In threatening situations the balance between sympathetic and parasympathetic stimulation is upset and the sympathetic becomes dominant

Situations that involve fear-anger, stress, danger or competition provoke what is called a fight-or-flight response or alarm reaction

These responses prepare the body for increased activity

activation of sympathetic nervous system include:
- increase heart rate and force of contraction
- dilation of blood vessels in neccessary organs: liver,
heart, skeletal muscles
- dilation of airways in the lungs and increased depth and
rate of breathing

Question 23

what are ‘receptors’

Answer 23

Structures within the cell membrane that are capable to detect a change in the body’s internal or external environments

Question 24

list some different types of receptors

Answer 24

osmoreceptors

chemoreceptors

touch receptors

pain receptors

thermoreceptors

Question 25

explain what an osmoreceptor is

Answer 25

detect osmotic pressure/water balance. Located in the hypothalamus

Question 26

explain what an chemoreceptor is

Answer 26

detect specific chemicals Detect smell and taste in the nose and mouth Detect oxygen, carbon dioxide and pH in blood vessels, and are involved in the regulation of heartbeat and breathing rate

Question 27

explain what an thermoreceptor is

Answer 27

detect heat and cold In skin – detect external temperatures In hypothalamus – detect internal body temperature

Question 28

what is a reflex

Answer 28

Rapid, automatic response to a change in the external or internal environment mostly coordinated by spinal cord The impulse may be passed to motor neurons at the same level in the cord, or may travel a few segments up or down the cord before travelling out through a motor neuron In these cases the reflex is carried out by the spinal cord and is known as a spinal reflex

Question 29

what are the 4 properties of reflexes

Answer 29

A stimulus is required Involuntary Rapid response Stereotyped

Question 30

what is a reflex arc

Answer 30

The pathway a nerve impulse follows in travelling from a receptor to an effector or in the case of a spinal reflex, a spinal reflex arc

Question 31

what are the components (what happens) in a reflex arc

Answer 31

The receptor reacts to a change in the internal or external environment by initiating a nerve impulse in the sensory neuron. A sensory neuron carries impulses from the receptor to the CNS There is at least one synapse. The nerve impulse may be passed directly to a motor neuron or there may be one or more interneurons A motor neuron carries the nerve impulse to an effector – away from CNS An effector receives the nerve impulse and carries out the appropriate response. Effectors are muscle cells or excretory cells.

Question 32

what are learned reflexes

Answer 32

More complex motor patterns appear during a baby’s development – e.g. sucking, chewing, following movement with eyes These innate reflexes are determined genetically Some complex motor patterns are learned and are called acquired reflexes They are learned through constant repetition

Question 33

what is the difference between the somatic and autonomic nervous system

Answer 33

SOMATIC: - carries message to skeletal muscles - neurotransmitter used is acetylcholine - one nerve fibre from CNS to effectors - no ganglion and synapse - voluntary AUTONOMIC: - carries messages to involuntary muscles and glands - neurotransmitter used is acetylcholine or noradrenline - 2 nerve fibres from CNS to effector - with a synapse in a ganglion - involuntary