chapter 13: nervous system

Question 1

what is the role of the nervous system in humans?

Answer 1

• controls the activities of the body and how it reacts to the surroundings ( the stimuli)
  > consists of: well-developed brain, spinal cord, spinal nerves and highly specialised sense organs

sense organs:
- help the body to adjust rapidly to any changes in the environment
- enable the various parts of the body to coordinate with one another quickly

• activities that are not controlled consciously and are automatic > INVOLUNTARY ACTIONS
  > eg. heartbeat, peristalsis and breathing
• activities controlled consciously > VOLUNTARY ACTIONS

Question 2

what are the components of the human nervous system?

Answer 2

nervous system made of:
- the central nervous system (CNS): brain and spinal cord
- the peripheral nervous system (PNS): cranial nerves from the brain, the spinal nerves from the spinal cord and the sense organs

-sense organs receive stimuli > called receptors
> inform the central nervous system of any change in surroundings
> by producing electrical messages called NERVE IMPULSES
- nerve impulses are transmitted to the central nervous system by nerves

• nerve impulse is transmitted within a fraction of a second
• in response to stimulus, the CNS will send nerve impulses to the muscles
  > muscles will then effect an action
  > known as EFFECTORS

Question 3

What does the nervous tissue consist of and what are the functions?

Answer 3

1. SENSORY NEURONE
   ( receptor neurone)
   - transmit nerve impulses from the receptors to the central nervous system
2. RELAY NEURON
   ( intermediate neuron)
   - transmit nerve impulses from the sensory neurone to the motor neuron
   > also found within the central nervous system
3. MOTOR NEURONE
   (effector neurone)
   - transmits nerve impulses from the central nervous system to the effectors

Question 4

what is a nerve fibre?

Answer 4

• a strand of cytoplasm extending from the cell body

Question 5

what is the cell body?
(structure of a motor neurone)

Answer 5

• it contains a nucleus, cytoplasm, cell surface membrane and organelles
• the cell body of the motor neuron is irregular in shape

Question 6

what is a dendron?
(structure of a motor neurone)

Answer 6

• dendrons are nerve fibres that transmit nerve impulses toward the cell body
  > a motor neuron has many
  > the end branches are called dendrites
• dendrites of a dendron receive nerve impulses from other neurones

Question 7

what is an axon?
(structure of a motor neurone)

Answer 7

• nerve fibres that transmit nerve impulses away from the cell body
  > axons in motor neurone are usually long

Question 8

what is a myelin sheath?
(structure of a motor neurone)

Answer 8

• the layer of fatty substances enclosing many nerve fibres
  > insulates the axon
  > like a rubber sheath would insulate an electricity-conducting wire

Question 9

what is the node of Ranvier?
(structure of a motor neurone)

Answer 9

• the region where the myelin sheath is absent
• nerve impulses cannot be transmitted through the myelin sheath
  > so they ‘jump’ from one node to the next
  > helps speed up the transmission of impulses along the nerve fibre

Question 10

what are axon terminals?
(structure of a motor neurone)

Answer 10

• the axon terminals of a motor neurone transmit nerve impulses to the effector

Question 11

what is the motor end plate?
(structure of a motor neurone)

Answer 11

• the junction between the axon terminals and the muscle fibre
• nerve impulses are transmitted across the motor end plate by chemicals which stimulate the muscles

Question 12

what is a synapse?

Answer 12

• a junction between two neurones, or a junction between a neuron and an effector
  > such as muscle or a gland
• at a synapse, impulses are transmitted from the axon of one neuron to the dendron of another neuron ( or cells of effector)
  > across a tiny space
• nerve impulses are transmitted across the synapse by chemicals released by the neuron
  > NEUROTRANSMITTERS

Question 13

what are nerves?

Answer 13

• a bundle of nerve fibres enclosed in a sheath of connective tissue
  > nerves may emerge from the brain (cranial nerve) or spinal cord (spinal nerve)

they may contain:
- sensory nerve fibres only
> conduct nerve impulses from sense organs

• motor nerve fibres only
  > such nerves conduct nerve impulses to effectors
• mixed fibres > both sensory and motor nerve fibres
  > spinal nerves contain mixed fibres

Question 14

what is reflex action?

Answer 14

• an immediate response to a specific stimulus without conscious control

Question 15

what does the central canal contain?

Answer 15

• the central canal contains a fluid
  > CEREBROSPINAL fluid
  > brings nutrients to the spinal cord

Question 16

what is the grey matter?

Answer 16

• it consists mainly of cell bodies of neurones
  > forms the outer layers of the brain and the central parts of the spinal cord

Question 17

what is the white matter?

Answer 17

> consists of mainly nerve fibres
forms the central parts of the brain
and the outer parts of the spinal cord

Question 18

why can you feel the coldness when you touch ice?
(sensation)

Answer 18

• temperature receptor in your skin is stimulated
  > impulses are produced
  > impulses are transmitted to the forebrain
• brain interprets the impulses and you have the sensation of coldness.

pathway of impulses:
- receptor in the skin
> sensory neuron
> relay neuron in the spinal cord
> forebrain

Question 19

what is voluntary action?

Answer 19

• a deliberate action, under control of the conscious will

> eg. you decide to raise your hand to answer a qn

• impulses produced by the forebrain
  > impulses are transmitted by a relay neurone from the forebrain
  > down the white matter of the spinal cord
  > into the to the grey matter
• in the grey matter, impulses are transmitted to the motor neurone which transmits the impulses to the effector muscles in your arm
  > muscles contracts and your hand is raised

pathway of impulses:
forebrain
> relay neurone in spinal cord
> motor neurone
> effector

Question 20

spinal cord and brain are REFLEX CENTRES
what can reflex actions be classified as?

Answer 20

cranial reflexes:
- controlled by the brain ( not the conscious will)
> usually occur in head region
>eg. pupil reflex, blinking and salivation

spinal reflexes:
- controlled by the spinal cord
>eg. knee-jerk reflex and sudden withdrawal of hand touching hot object

Question 21

what happens when your hand touches a hot object?

Answer 21

1. receptors in skin
   - the heat on the objects stimulates nerve endings ( receptors) in skin
   > nerve impulses produced
2. sensory neurone
   - the nerve impulses travel along sensory neurone to your spinal cord
3. spinal cord
   - nerve impulses are transmitted first across a synapse
   > to the relay neurone and then across another synapse to the motor neurone
4. motor neurone
   - the motor neurone transmits the nerve impulses from the spinal cord to the effector
5. effector muscle contracts
   - bicep muscles (effector) then contracts
   > causes hand to withdraw suddenly

Question 22

what is the reflex arc?

Answer 22

• the shortest pathway by which nerve impulses travel from the receptor to the effector in a reflex action

Question 23

what does a reflex arc consist of?

Answer 23

1. a receptor or sense organ
2. a sensory neurone
3. CNS (brain or spinal cord)
4. a motor neurone
5. an effector (muscle or gland)

Question 24

what are the differences between a motor neurone and a sensory neurone?

Answer 24

sensory neurone:
- regular cell body
- transmit nerve impulses from receptor to CNS
- shorter axons and longer dendrons

motor neurone:
- irregular cell body
- transmit nerve impulses from CNS to effector
- longer axons and shorter dendrons