Divisions of the Nervous System

Question 1

Neurons & the nervous
system

Answer 1

The nervous system is comprised of several connected
systems:
- The Central Nervous System (CNS) = BRAIN & SPINAL
CORD
- The Peripheral Nervous System (PNS) = SOMATIC &
AUTONOMIC NERVOUS SYSTEMS

Question 2

The Central Nervous System (CNS)

Answer 2

The CNS comprises of the brain and the spinal cord.

Question 3

The brain has four main areas:

Answer 3

• the cerebrum: main outer layer of the brain. split in two halves. divided into four main areas; frontal lobe for
  thought, occipital lobe for vision, motor cortex for movement and auditory cortex for speech.
• the cerebellum: motor skills and balance
• the diencephalon: comprises the thalamus (relay station sending nerve impulses from senses to correct area of brain for processing) and the hypothalamus (memory, hunger, thirst)
• the brain stem: regulates automatic functions e.g. breathing

Question 4

The spinal cord

Answer 4

an extension of the brain.
It acts as a relay between the brain and body.
It also contains simple relay neurons which help us to perform
quick, reflexive actions which don’t involve the brain, e.g. pulling
your hand away from something hot.

Question 5

The Peripheral Nervous System

Answer 5

The PNS refers to all nerves outside of the CNS. Its function is to relay impulses to and from the CNS and the rest of the body. There are two subdivisions: Autonomic nervous system and the somatic nervous system.

Question 6

Autonomic nervous system (1)

Answer 6

The control of involuntary actions. Some are excitatory (and involve the sympathetic division of the ANS which is involved in fight or flight primarily) and some are inhibitory (which involve the parasympathetic division which brings the body back to
a restful state after an emergency)

Question 7

The somatic nervous system (1)

Answer 7

Made up of 12 pairs of cranial nerves and 31 pairs of spinal
nerves. Sensory nerves relay messages to CNS and motor neurons from CNS to the body.

Question 8

Autonomic nervous system (2)

Answer 8

Plays an important role in homeostasis, which maintains internal processes like body temperature, and blood pressure.
Only consists of motor pathways and has two components:
- The sympathetic nervous system is typically involved in responses that prepare the body for fight or
flight.
- The role of the parasympathetic nervous system is to relax the body, and return us to our ‘normal’
resting state.

Question 9

The somatic nervous system (2)

Answer 9

Made up of sensory receptors that carry information to
the spinal cord and brain, and motor pathways that allow the brain to control movement.
Therefore, the role of the somatic nervous system is to carry sensory information from the outside world to the brain and provide muscle responses via the motor pathways.
As well as controlling behaviour it regulates physiological processes.

Question 10

Neurons

Answer 10

Neurons provide the nervous system a
means of communication chemically and
electrically. Of the 100 billion neurons, 80%
are found in the brain.

Question 11

Types of Neurons & their functions

Answer 11

• Neuron? = a general term for a nerve cell that processes & transmits messages via electrical and chemical signals
• Sensory neuron? – carry messages from the pns to the cns (lots of them in extremities!) Long dendrites and short axons
• Relay neurons? – connect sensory neurons to motor or relay neurons. Short dendrites & short axons
• Motor neurons? – connect cns to muscles and glands. Short dendrites & long axons

Question 12

The structure of a neuron

Answer 12

• Vary in size but same structure.
• Cell body (soma) includes a nucleus which contains the genetic material of the cell.
• Dendrites (branch-like structures) protrude from the cell body.
• Axon carries the impulse away from the cell body down the length of the neuron.
• Axon is covered in a fatty layer of myelin sheath that protects the axon and speeds up electrical transmission of the impulse.
• Myelin sheath is segmented by gaps called nodes of Ranvier; these speed up the transmission of the impulse by forcing it to ‘jump’ across the gaps along the axon.
• Terminal buttons (end of axon) - communicate with next neuron in the chain across a gap known as the synapse.

Question 13

Synaptic Transmission

Answer 13

The process by which neighbouring neurons communicate by sending chemical messages across the synapse (gap between them).

Question 14

Electrical transmission

Answer 14

• When a neuron is in a resting state inside of the cell is negatively charged compared to the outside.
• When a neuron is activated by a stimulus the inside of the cell becomes positively charged for a split second causing an action potential to occur.
• This creates an electrical impulses that travels down the axon towards the end of the neuron.

Question 15

Reuptake of Neurotransmitters

Answer 15

After the messages have been sent, any leftover neurotransmitters can be recycled.
The effect of a neurotransmitter is lessened when the message has been received by the postsynaptic neuron and during reuptake.

Question 16

Neurotransmitters (1)

Answer 16

Several neurotransmitters exist in the brain. Some of the main ones that do most of the work are:
Dopamine (DA)? – motivation, reward, stimulation
Serotonin (5-HT)? – mood stabilising, calm
Adrenaline? – fight or flight response

Question 17

Neurotransmitters (2)

Answer 17

• Neurotransmitter - Brain chemicals released from synaptic vesicles that relay signals across the synapse from one neuron to another. Neurotransmitters can be broadly divided into those that perform an excitatory function and those that perform an inhibitory function.
• Excitation - When a neurotransmitter, such as adrenaline, increases the positive charge of the postsynaptic neuron. This increases the likelihood that the neuron will fire and pass on the electrical impulse. This is called an excitatory postsynaptic potential (EPSP).

Question 18

Neurotransmitters (3)

Answer 18

• Inhibition? - when a neurotransmitter, such as serotonin, makes the charge of the postsynaptic neuron more negative. This decreases the likelihood that the neuron will fire and pass on the electrical impulse. This is called an inhibitory postsynaptic potential (IPSP).
• Summation? - Excitatory and inhibitory influences are summed and must reach a certain threshold in order for the action potential of the postsynaptic neuron to be triggered. If the net effect of the neurotransmitters is inhibitory then the postsynaptic neuron is less likely to fire (i.e. no electrical signal is transmitted). It is more likely to fire if the net effect is excitatory.