Unit 2 - Nervous System

Question 1

structure & function of a neuron: cell body, dendrites, axon, myelin sheath, Schwann cell, node of ranvier, neurilemma

Answer 1

Cell Body - contains nucleus - responsible for controlling the functioning of the cell
Dendrites - Short extensions - carry nerve impulses into cell body
Axon - carries nerve impulses away from the cell body
Myelin sheath - insulates, protects and speeds up the movement of impulses along the axon
Schwann Cell - forms the myelin sheath only within the PNS
Node of Ranvier - facilitates the rapid transmission of nerve impulses
Neurilemma - outermost coil of Schwann cells

Question 2

Neurons classified by function

Answer 2

sensory - carry messages from receptors in the sense organs, or in the skin, to the central nervous system
Motor - carry messages from the CNS to effectors
Interneurons - link between the sensory and motor neuron

Question 3

Define nerve impulse (3)

Answer 3

• the message that travels along a nerve fibre
• transmission of a nerve impulse triggers an action potential in the adjacent membrane
• Impulse conducts along unmyelinated fibres through salatory conduction (jumping conduction - jumps from one NOR to another)

Question 4

transmission of a nerve impulse

Answer 4

Polarisation
○ At a resting, potential the membrane is polarised
○ inside of the cell and has a net negative charge and the outside of the cell has a net positive charge.
○ A Na/K pump allows these ions to move across the membrane: sodium into the cell and potassium out
Depolarization
○ the sudden increase in membrane potential
- ligand-gated channels open
○ If the stimulus is strong enough to increase the potential to -55mV then voltage-gated sodium channels open
○ This produces a movement of sodium ions into the cells
○ The size of the response is not related to the strength of the stimulus, this is also known as the all or none response)
Repolarization
○ The sodium channels close, which stops the influx of sodium ions
○ At the same time, voltage-gated potassium channels open, increasing the flow of potassium ions out of the cell
○ This makes the inside of the membrane more negative than the outside and decreases the membrane potential
○ The membrane is repolarized
○ The potassium channels remain open longer than what is needed, this results in the membrane potential dropping lower than the resting membrane potential, and the membrane is hyperpolarized
○ This process is called hyperpolarization
4) Refractory Period
○ Once the sodium channels have opened they quickly become inactivated
○ Thus being unresponsive to stimulus
○ Therefore, for a brief period after being stimulated, the membrane will not undergo another action potential

Question 5

Transmission across a synapse

Answer 5

1. Nerve impulse reaches the axon terminal, it activates voltage gated calcium ion channels
2. As there is a higher concentration of calcium ions in the extracellular fluid, they flow into the cell at the pre-synaptic axon terminal
3. This causes synaptic vesicles to fuse with the membrane, releasing special chemicals called neurotransmitters by exocytosis
4. The neurotransmitters diffuse across the gap and attach to receptors on the membrane of the next neuron
5. This stimulates ligand-gated protein channels to open, which allows the influx of sodium ions an initiates an action potential

Question 6

conduction along unmyelinated fibres (3)

Answer 6

1. depolarisation of one area causes depolarisation in another area of the membrane
2. this movement stimulates the opening of voltage-gated sodium channels, initiates action potential in the membrane
3. refractory period prevents the impulse going backward as action potential cannot be generated

Question 7

transmission along myelinated fibres

Answer 7

1. myelinated fibres prevents the diffusion of ions through the membrane
2. action potential jumps from one node to another (as it is unmyelinated)
3. saltatory conduction = faster

Question 8

thermoreceptors

Answer 8

• sensitive to heat & cold
  peripheral in the skin informs the brain (hypo & cerebrum)

Question 9

osmoreceptors

Answer 9

• in the hypo (thirst centre)
• sensitive to concentration of substances in water (osmotic pressure)

Question 10

chemoreceptors

Answer 10

• mouth (taste) nose (odour)
  peripheral (aortic & carotid bodies)
  *body fluids e.g. pH, CO2, O2
  central (medulla)
• CO2 & pH

Question 11

nociceptors

Answer 11

• stimulated by damages to the tissue e.g. poor blood flow, excessive stimuli such as heat

Question 12

touch receptors

Answer 12

• surface of the skin, sensitive to touch, nerve endings & follicles
• others located deep down sensitive to vibrations & pressure

Question 13

Central Nervous System Protection

Answer 13

Bone - cranium and vertebral canal
Meninges - duramater, arachnoidmater and pia mater
CSF - clear watery fluid

Question 14

Describe the layers of the meninges

Answer 14

○ Dura mater - outermost layer, tough and fibrous, texture and thickness similar to rubber glove
○ Arachnoid mater - loose mesh of fibres - resembles web
Pia mater - inner layer, delicate - contains many blood vessels and sticks closely to the surface of the brain and spinal cord

Question 15

What are the three main functions of the CSF

Answer 15

1. Protection - acts as a shock absorber
2. Support - brain floats inside it
3. Transport - CSF is formed from the blood, and circulates around and through the CNS before eventually re-entering the blood capillaries. During its circulation it takes nutrients to cells of the brain and spinal cord

Question 16

Describe the different parts of the brain - cerebrum, medulla obligate, cerebellum and corpus calloscum

Answer 16

Cerebrum - responsible for thinking, reasoning, learning, memory and sense of responsibility. Has a large surface area due to its folded structure.

Medulla oblongata - joins the brain to the spinal chord

Cerebellum - part of the brain behind and below the cerebrum; concerned with coordination of movement

Corpus callosum - bundle of nerve fibres that links the two cerebral hemispheres

Question 17

Divisions of the PNS

Answer 17

Afferent( sensory)
Efferent (motor) ->1. Somatic 2. Autonomic -> Sympathetic & Parasympathetic

Question 18

What is the structure and function of the autonomic and somatic nervous system

Answer 18

Autonomic
Structure - groups of nerve cells in the medulla oblongata, hypothalamus and cerebral cortex
Function - controls the body’s internal environment and is involved in many of the mechanisms that keep it constant

Somatic
Structure - nerves and neurons
Function - responds to the external environment

Question 19

what is the structure and function of the sympathetic and parasympathetic nervous system

Answer 19

Parasympathetic
Function - generally produces responses that maintain the body during relatively quiet condition

Sympathetic
Function - produce responses that prepare the body for strenuous physical activity

Question 20

Compare how the afferent and efferent nervous system detects and responds to changes in the internal and external environments

Answer 20

Afferent
- Internal
carries impulses into the CNS from receptors in the skin
- External
notifies internal of impulses

Efferent
- Internal
carries impulses away from the CNS
- External
takes impulses from the somatic and autonomic PNS

Question 21

Compare how the autonomic and somatic nervous system detects and responds to changes in the internal and external environments

Answer 21

Autonomic
- Internal
adjustment of the internal environment - affects heart muscles, involuntary muscle, and glands
- External
No detection

Somatic
- Internal
no detection
- External
responds to the external environment - effects skeletal muscles

Question 22

Compare how the sympathetic and parasympathetic nervous system detects and responds to changes in the internal and external environments

Answer 22

Sympathetic
- Internal
everything from above and blood vessels of skin, skeletal muscle and internal organs
- External
no detection
Parasympathetic
- Internal
Heart, lungs, stomach and intestines, liver, iris, salivary gland, and urinary bladder
- External
no detection

Question 23

Q
what specific parts of the central nervous system have roles in the co-ordination of body functions and are protected by the bones of the skull, the meninges and cerebro-spinal fluid

Answer 23

Brain - cerebrum, cerebellum, medulla oblongata, hypothalamus, corpus callosum

Spinal cord

Question 24

what specially structured neurons are in the reflex arc and are used to transmit information from the receptor to the effect

Answer 24

Sensory (PNS)
Interneurons (CNS)
Motor (PNS)

Question 25

nervous vs endocrone

Answer 25

nervous
*rapid
*short lasting
*utilises electrical impulses
*influence one effector
endocrine
*slower
*long lasting
*utilises hormones
*affects number of diff organs

Question 26

how does the central nervous system relay neurons

Answer 26

Through its interneurons, which as the same suggest connects sensory and motor neurons by going in between them.

Question 27

How do osmoreceptors detect changes in the internal and external environments?

Answer 27

Internal - determines osmotic pressure
- determined by the concentration of substances dissolved in the water of the blood plasma
- located in the hypothalamus and are sensitive to even very small changes

Question 28

How do chemoreceptors detect changes in the internal and external environments?

Answer 28

Internal
- sensitive to the pH of the blood and to the concentrations of oxygen and CO2
External
-Present in nose, causing smell and present in mouth causing taste

Question 29

How do touch receptors detect changes in the internal and external environments?

Answer 29

External
- nerve endings send impulses to the brain

Question 30

How do pain receptors detect changes in the internal and external environments?

Answer 30

External and Internal
- stimulated by damage to the tissues
- occurs everywhere but brain

Question 31

How does the parasympathetic division effects its target organs

Answer 31

Heart - decrease rate and strength of contraction
Lungs - constricts bronchioles
Stomach, intestines - increases movement
Liver - increases uptake of glucose and synthesis of glycogen
Iris - constricts pupil
Sweat - no effect
Salivary glands - increases secretion of saliva
Blood vessels - little to no effect
Urinary bladder - constricts muscles of wall
Adrenal medulla - no effect

Question 32

describe the spinal cord structure

Answer 32

• white matter surround the grey matter in the centre arranged in bundles called tracts
  ascending tract:
  *sensory axons that carry impulses towards the brain
  descending
  *motor axons carry impulses away from the brain

Question 33

spinal cord function

Answer 33

• carry sensory impulses up, motor impulses down
• integrate fast automatic responses aka reflex

Question 34

what is the structure and function of the central and peripheral nervous system

Answer 34

Central
Structure - brain and spinal chords - protected by bone, meninges and cerbrospinal fluid
Function - receives and processes incoming messages and outgoing messages are initiated

Peripheral
Structure - cranial nerves and spinal nerves
Function - takes messages from receptors to the CNS and from the CNS to muscles and glands

Question 35

what is the structure and function of the afferent and efferent nervous system

Answer 35

Afferent
Structure - nerves and neurons
Function - carry impulses into the CNS

Efferent
Structure - nerves and neurons - carry away from the CNS - divided into somatic and autonomic
Function - carry impulses away from the CNS

Question 36

What is the structure and function of the autonomic and somatic nervous system

Answer 36

Autonomic
Structure - groups of nerve cells in the medulla oblongata, hypothalamus and cerebral cortex
Function - controls the body’s internal environment and is involved in many of the mechanisms that keep it constant

Somatic
Structure - nerves and neurons
Function - responds to the external environment

Question 37

what is the structure and function of the sympathetic and parasympathetic nervous system

Answer 37

Parasympathetic
Function - generally produces responses that maintain the body during relatively quiet condition

Sympathetic
Function - produce responses that prepare the body for strenuous physical activity

Question 38

how does the sympathetic division effect its target organs

Answer 38

Heart - increases rate and strength of contraction
Lungs - dilates bronchioles
Stomach - decreases movement
Liver - increases breakdown of glycogen and release of glucose
Iris - dilates pupil
Sweat Glands - increases sweat secretion
Salivary glands - decreases secretion of saliva
skin blood vessels - constricts vessels
Skeletal muscle blood vessels - dilates
Internal organ blood vessels - constricts
Urinary bladder - relaxes muscles of wall
Adrenal medulla - stimulate hormone secretion