BP - The nervous system

Question 1

What is the Central Nervous System?

Answer 1

Part of the nervous system, consisting of primarily the brain and spinal cord. Controls most functions of the body and mind - the brain is the center of our thoughts, interpreter of our external environment and the origin of control over body movement.

Question 2

What is the Peripheral Nervous System?

Answer 2

Parts of the nervous system outside the brain and spinal cord; all the other nerves in the body. Composed of two subdivisions.

Question 3

Somatic Nervous System

Answer 3

The voluntary NS - one of the subdivisions of the PNS associated with the voluntary control of body movements via skeletal muscles.

Question 4

Autonomic Nervous System`

Answer 4

Part of the PNS involved in involuntary physiological processes with anatomically distinct divisions - sympathetic and parasympathetic

Question 5

Sympathetic Nervous System

Answer 5

Controls fight or flight responses or stress responses; prepares the body for action by increasing heart rate, breathing rate and stops digestive and reproductive function. Primarily involved in responses that help us deal with emergencies and responds to perceived threat. Neurons from the SNS travel from every organ and gland within the body to produce physiological changes to prepare the body for flight or fight.

Question 6

Parasympathetic nervous system

Answer 6

Restores normal physiological function when the threat has passed and because the PNS is involved with energy conservation and digestion, it is sometimes referred to as the body’s rest and digest system.

Question 7

The Nervous System

Answer 7

A specialised network of nerves in the human body and is our primary internal communication system, allowing body to communicate.
Two main functions - collect, process and respond to information in the environment and coordinate the working of different organs and body cells

Question 8

Afferent neurons (sensory neurons)

Answer 8

Carry information to the CNS

Question 9

Efferent neurons (motor neurons)

Answer 9

Carry information away from the CNS

Question 10

Diagram of the division of the nervous system

Answer 10

Human Nervous System ->
Central Nervous System / Peripheral Nervous System
->
CNS = Brain and Spinal Cord
PNS = Autonomic Nervous System and Somatic Nervous System
->
ANS = Parasympathetic nervous system and Sympathetic nervous system

Question 11

Neuron Structures

Answer 11

1. Axon terminal - they communicate with the next neuron on the chain across the synapse; in motor neurons, this is where the response is initiated.
2. Myelin Sheath - this is fatty layer that protects the axon and speeds up electrical transmission of the action potential
3. Axon - Carries action potentials away from the cell body down the length of the neuron
4. Soma (cell body) - this is the control centre of the neuron
5. Nucleus - contains genetic material of the cell
6. Dendrites - these carry nerve impulses from neighboring neurons or sensory receptors to the cell body
7. Nodes of Ranvier - Gaps in the myelin sheath that speed up transmission of the action potential by facing the impulse to jump across the gaps along the axon

Question 12

Neurons

Answer 12

• Cells of the nervous system that process and transmit messages through electrical and chemical signals
• Specialised cells which move electrical impulses to and from the CNS
• Electrical impulses are called action potentials
• When a neuron is in a resting state, the inside of the cell is negatively charged in comparison to the outside
• When a stimulus activates the neuron, the inside becomes positively charged for a split second causing an action potential to occur - this causes the electrical impulse to travel down the axon towards the end of the neuron

Question 13

How the system communicates through the neurons - diagram

Answer 13

Stimulus -> Sensory receptor -> Sensory neuron -> Relay neuron -> Motor neuron -> Effector -> Response

Question 14

Features of motor neurons

Answer 14

• Connect the CNS too effectors such as muscles and glands
• They are located in the CNS and their axons project outside the CNS directly or indirectly to control muscles
• When the axon of the neuron fires, the muscles with which it forms synapses contracts; when the neuron is inhibited, the muscle relaxes
• They have short axons and long dendrites
• They send messages via long axons from the brain to the muscles or effectors
• They form synapses with muscles and control their contractions; when stimulated, they bind to receptors on the muscle and trigger a response which leads to muscle movement

Question 15

Features of sensory neurons

Answer 15

• Carry messages from sensory receptors via the PNS to the CNS
• They convert information from sensory receptors into neural impulses
• They have long dendrites and short axons
• Not all sensory information travels as far as the brain, with some of these neurons terminating in the spinal cord - this allows reflex actions too occur quickly without the delay of sending impulses to the brain

Question 16

Features of relay neurons

Answer 16

• They have long axons and short dendrites
• When the impulses reach the brain, they are translated into sensations so that the organism can decide how to respond appropriately
• They are only found within the brain and spinal cord (CNS)
• They connect with other neurons, allowing sensory and motor neurons to communicate with each other

Question 17

An example of neuron interaction - knee jerk reflex arc

Answer 17

1. A stimulus, such as a hammer, hits the knee
2. This is detected by sense organs in the PNS, which convey a message along a sensory neuron
3. This message reaches the CNS, where it connects with a relay neuron.
4. This then transfers the message to a motor neuron
5. This then carries the message to an effector, such as a muscle, which causes the muscle to contract and therefore cause the knee to move or jerk

Question 18

Structures of a Synaptic Knob

Answer 18

• Terminal button - the entire structure
• Neurotransmitters - located within the synapse, (small round chemicals)
• Synapse - the bulb shaped structure
• Synaptic vesicles - located inside the synapse, contain the neurotransmitters
• Dendrite - what the synapse connects too (the neighboring neuron)
• Synaptic gap / cleft - the space between the synapse and dendrite the neurotransmitter moves across to transfer the electrical impulse information
• Terminal button membrane / pre-synaptic membrane; the surrounding membrane of the synapse allows the neurotransmitters out
• Post-synaptic receptor sites - the semicircular spaces in the dendrite where the neurotransmitter is received from the synapse

Question 19

Neural networks and the transmission of signals

Answer 19

• Neurons communicate with each other within groups known as neural networks
• Each neuron is separated from the next by a tiny gap called the synapse
• Signals within the neurons are transmitted electrically (fast movement)
• Signals between neurons are transmitted chemically across the synapse in the process of synaptic transmission (chemical = slows it down)
• Chemicals diffuse across the synaptic gap or cleft
• Electrical impulse -> chemical -> electrical

Question 20

The process of synaptic transmission

Answer 20

1. When the action potential reaches the pre-synaptic terminal it trigger the synaptic vesicles to release (electrical impulse transfers into chemical) neurotransmitters into the synaptic gap
2. The neurotransmitters diffuse across the synaptic gap between pre and post synaptic cells
3. The neurotransmitters bind to the post-synaptic receptor sites in the membrane of the post-synaptic neuron’s dendrite
4. The stimulation of the post-synaptic receptors converts the chemical messages back to one electrical impulse and the process of transmission begins again in the post-synaptic neuron
5. The effects are terminated by a process called reuptake; the neurotransmitters are taken up by the pre-synaptic neuron where they are again stored in synaptic vesicles ready for later release, or are recycled for future chemical diffusion

Question 21

Synapse

Answer 21

The area at the end of a neuron that holds the neurotransmitters ready synaptic transmission.
The electrical impulses are passed from the pre-synaptic neuron to the post-synaptic neuron
The synaptic gap, or cleft, is able to modify the reaction

Question 22

Dendrites

Answer 22

The area at the start of the neuron that receives that synaptic transmission and converts it back into an electrical impulse before sending it down the axon of the nerve to the next synapse for continued transmission of information and electrical impulses.

Question 23

Excitatory and inhibitory neurotransmitters

Answer 23

• Neurotransmitters can be excitatory (adrenaline +) or inhibitory (serotonin -)
• If it is excitatory, this causes excitation of the post-synaptic membrane (excitatory postsynaptic potentials or EPSPs / depolarisation), increasing the likelihood of the post-synaptic neuron firing an electrical impulse as depolarisation causes the release of action potentials (- switches to +)
• If the neurotransmitter is inhibitory, this causes inhibition of the post-synaptic membrane (inhibitory post-synaptic potentials or ISPSs / hyperpolarization) decreasing the likelihood of the post-synaptic neuron firing an electrical impulse

Question 24

E and I neurotransmitters cont.

Answer 24

The excitatory and inhibitory influences are summed (summation); if the net effect on the post-synaptic neuron is inhibitory, the neuron will be less likely to fire and if the net effect is excitatory, the neuron will be more likely to fire (an action potential, so it is useful for neurons to be excitatory)

Question 25

Parts of the brain - The cerebrum

Answer 25

• the largest part of the brain
• Divided into 4 different lobes; frontal, occipital, parietal and temporal
• includes the cerebral cortex, the brain’s outer layer; this is responsible for higher mental functions such as conscious decision making
• Split into two cerebral hemispheres, with each one being specialized into specific behaviors and the two halves communicate with each other via the corpus callosum

Question 26

Parts of the brain - The cerebellum

Answer 26

• Located at the back of the cerebrum
• Involved in controlling a person’s motor skills, balance and coordinating the muscles to allow precise movements
• Abnormalities of this area can result in a number of problems, including speech, motor problems and epilepsy

Question 27

Parts of the brain - the diencephalon

Answer 27

• Lies beneath the cerebrum on the top of the brain stem
• Contains the thalamus and hypothalamus
• Thalamus - relay station for nerve impulses coming from the senses, routing them to the appropriate part of the brain where they can be processed
• Hypothalamus - regulation of body temperature, hunger and thirst, acting as a link between the endocrine and nervous system controlling the release of hormones from the pituitary gland

Question 28

Parts of the brain - the brain stem

Answer 28

• Lies at the base of the brain
• Responsible for regulating the automatic functions that are essential for life
• Includes breathing, heartbeat and swallowing
• Motor and sensory neurons travel through the brain stem, allowing impulses to travel between the brain and spinal cord

Question 29

Synaptic transmission - the full process

Answer 29

1. Action potential reaches the pre-synaptic terminal
2. This triggers the synaptic vesicles to release neurotransmitters into the synaptic gap
3. These neurotransmitters are either inhibitory or excitatory
4. The neurotransmitters diffuse across the synaptic gap between the pre and post-synaptic cells
5. The neurotransmitters bind to the post-synaptic receptor sites on the membrane of the post-synaptic neuron’s dendrite
6. this stimulation of the post-synaptic receptors converts the chemical message back to the electrical impulse
7. The process of transmission begins again in the post-synaptic neuron
8. If the neurotransmitter is excitatory, this causes excitation of the post-synaptic membrane, and so the post-synaptic membrane is more likely to fire the action potential
9. If the neurotransmitter is inhibitory, this inhibits the post-synaptic membrane and so the post-synaptic neuron is less likely to fire an action potential
10. The excitatory and inhibitory influences are summed (summation) - if the net effect is excitatory, the action potential is fired, if it is inhibitory, it is not (stops overreaction)
11. The effects are terminated by a process called re-uptake - neurotransmitters are taken up by the pre-synaptic neuron where they are again stored in a synaptic vesicles ready for later release.