The Nervous System

Question 1

What are the parts of the nervous system ?

Answer 1

The central nervous system consists of the brain and the spinal cord

The Peripheral Nervous System consists of nerves that carry impulses from th CNS

Question 2

What are neurons?

Answer 2

“A neuron is a nerve cell”

A “Sensory Neuron” carries impulses from the receptors in sense organs to the CNS

A “motor neuron” carries impulses away from the CNS to muscles and glands

An “ interneuron” carries impulses within the CNS (ie.from sensory to motor neurons)

Question 3

What’s the function of different parts of the neuron?

Answer 3

Dendrites - receive information and carry electrical impulses swords the cell body

Axons - carry impulses away from th well body

Cell body - contains a nucleus and forms dendrites and axons

Myelin(sheath) - fat rich material that insulates the electrical impulses

Schwann cells - form the myelin (sheath)

Neurotransmitter swellings - Produce neurotransmitter chemicals

Question 4

What are the features of nerve impulses?

Answer 4

An impulse travels along a neuron in the form of an electrical impulses

In order for the electrical impulses to travel it is necessary for ions to move in and out of dendrites and axons

The movement of these ions requires energy in the form of ATP

Threshold:

” The threshold is the least possible stimulus needed to send an impulse”

An impulse will pass along a neuron if it receives a stimulus of sufficient strength

If the stimulus is below the threshold it will fail to cause an impulse to pass

Question 5

What is a synapse ?

Answer 5

“A synapse is the region where two neurons come into close contact, a synaptic cleft is the gap between two neurons”

Events at synapse:

• When an electrical impulse arrives at a synapse it stimulates the release of neurotransmitter chemicals(made and stored in neurotransmitter swellings). These swelling are found only at one side of the synapse (I.e they are on the sensory neuron)
• A lot of neurotransmitter chemicals made by the nervous system, ach dopamine - These chemicals diffuse across the synaptic cleft
• When the chemicals enter the motor neuron they are broken down by enzymes to generate an electrical impulse

Function of synapse
- controls the direction of impulses

Question 6

What is the central nervous system?

Answer 6

Consists of the the brain and the spinal cord

Enclosed by three membranes called the meninges

Protective fluid called cerebrospinal fluid is located between the inner two meninges

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Question 7

The Brain

Answer 7

Cerebrum
- it controls voluntary movement receives impulses from sense organs, intelligence, personality

• divided into two cerebral hemispheres connected by corpus callosum

Left controls right hand side of the body + maths, logic
Right controls left side of body + music, shapes, emotions

Cerebellum
- controls balance and muscle co ordination

Medulla
- controls involuntary muscles e.g. intercostal muscles, the diaphragm and intestinal muscles

Thalamus and hypothalamus

• Thalamus is the sorting centre of the brain, incoming impulses at directed to correct part of brain
• hypothalamus controls internal environment of the body (homeostasis), regulates hunger + thirst+ temperature +blood pressure

Question 8

The spinal cord

Answer 8

Carries impulses to and from the brain

Also involved in reflex actions

Parts and their functions

Meninges - surround and control the entry of materials into the brain and spinal cord

Spinal nerves - carry impulses to and from the spinal cord

Dorsal root - carries impulses into spinal cord along sensory neurons

Ganglion - swelling that contains the cell bodies of sensory neurons

White matter - contains axons

Grey matter - contains cell bodies

Central canal - contains fluid called cerebrospinal fluid

Ventral root - carries impulses out of the spinal cord along motor neurons

Question 9

What is a reflex ?

Answer 9

“A reflex action is an automatic unconcios or involuntary response to a stimulus”

Examples: - knee jerk, blinking for protection

The benefit of reflex actions is that they allow faster responses than normal

They protect the body from harm

Question 10

What’s the path of a reflex action ?

Answer 10

1. Receptors in the finger detect the hot object
2. An impulse travels along a sensory neuron to the spinal cord
3. The impulse travels into the spine through the dorsal root
4. In the spinal cord the impulse splits
   a) crosses a synapse into an interneuron
   b) crosses another synapse and passes up to brain
5. From interneuron it crosses another synapse and travels out of the central root along a motor neuron

Question 11

What is Parkinson’s disease ?

Answer 11

Caused by the failure to produce the neurotransmitter dopamine

Symptoms…

• trembling hands and legs
• muscular stiffness
• difficulty in walking

The Causes are unknown so there is now cure or way of preventing

Treatment includes physiotherapy and special exercises