Topic 5 - Nervous System

What is the main purpose of the nervous system?

The nervous system allows the body to work efficiently by:

• receiving information from inside and outside the body

• processing this information

• producing an appropriate response.

Why does the body need control and regulatory systems?

The body needs control and regulatory systems to ensure it works efficiently and effectively by coordinating responses and maintaining stable internal conditions.

What are the two main systems involved in control and regulation in the body?

1. The nervous system

2. The endocrine system

What are the two main divisions of the nervous system?

1. Central nervous system (CNS)

• Brain

• Spinal cord

2. Peripheral nervous system (PNS)

• All nerves outside the CNS.

What structures make up the central nervous system (CNS)?

• The brain

• The spinal cord

What is the function of the CNS?

• receives sensory information

• processes information

• sends responses to the body.

Where is the brain located and what are its main functions?

The brain is located inside the cranium (skull).

Functions include:

• movement

• sensation

• communication

• emotions

• thought processing

• memory.

Where is the spinal cord located and what is its function?

The spinal cord is located inside the spinal canal within the vertebral column.

Functions:

• sends sensory information from the body to the brain

• sends motor messages from the brain to the body.

What is the peripheral nervous system (PNS)?

The PNS consists of all nerves outside the central nervous system.

Its role is to connect the CNS with the rest of the body.

What are the three divisions of the autonomic nervous system?

1. Sympathetic nervous system

2. Parasympathetic nervous system

3. Enteric nervous system

What is the function of the sympathetic nervous system?

The sympathetic nervous system controls the body during emergencies.

It produces the fight or flight response, influenced by adrenaline.

What happens during the fight or flight response?

The body prepares for danger by causing:

• increased heart rate

• faster breathing

• sweating

• dry mouth.

What is the function of the parasympathetic nervous system?

It maintains the body during rest.

It controls:

• heart rate

• blood pressure

• digestion

• urination

• sweating.

What does the enteric nervous system control?

The enteric nervous system controls digestion by regulating:

• blood flow

• secretions

• hormone release

• movement of food through the digestive tract.

Describe the structure and location of the spinal cord.

• a long cylindrical organ

• located inside the spinal canal

• runs from the brainstem to the lower back

• contains a central cavity filled with cerebrospinal fluid (CSF).

What two types of messages does the spinal cord transmit?

1. Motor signals

• From the brain to the body.

2. Sensory information

• From the body to the brain.

How many pairs of peripheral nerves branch from the spinal cord?

31 pairs of peripheral nerves branch from the spinal cord.

What are sensory neurones?

Sensory neurones carry sensory information from receptors in the body through peripheral nerves to the CNS.

Information comes from the five senses:

• hearing

• sight

• smell

• taste

• touch.

What are motor neurones?

Motor neurones carry impulses from the CNS to muscles and glands to produce a response.

What is the difference between sensory and motor neurones?

Sensory neurone	Motor neurone
Carries information to CNS	Carries messages away from CNS
Receptors → brain/spinal cord	Brain/spinal cord → muscles/glands

What is a reflex action?

A reflex action is a rapid automatic response to a stimulus that happens without conscious thought.

Example:
Pulling your hand away from a hot surface.

Explain the reflex arc pathway.

• A receptor detects a stimulus (e.g. heat).

• Sensory neurone carries the impulse to the spinal cord.

• Relay neurone transfers the impulse.

• Motor neurone carries the impulse to the muscle.

• Muscle contracts and removes the hand.

Why is the brain considered the most complex organ in the body?

The brain is the most complex organ because it controls and coordinates many body functions, including:

• thought

• memory

• interpretation of senses

• movement

• regulation of body systems.

Different areas of the brain have different functions.

Where is the cerebrum located and what is its structure?

• is the outer layer of the brain

• covers the two hemispheres (left and right halves)

• is made of grey matter.

Each hemisphere contains six lobes:

• frontal

• parietal

• temporal

• occipital

• insular

• limbic.

What are the functions of the cerebrum?

The cerebrum is responsible for:

• problem-solving

• learning

• memory

• emotions

• decision-making

• motor functions

• sensory functions.

Where is the cerebellum located?

• at the back of the skull

• in the hindbrain

• below the cerebrum

• near the brainstem.

What are the functions of the cerebellum?

The cerebellum:

• maintains posture and balance

• coordinates movement.

It receives information from:

• joints

• muscles

• cerebrum.

Where is the brainstem located and what structures make it up?

The brainstem is located:

• in front of the cerebellum

• at the bottom of the brain.

It consists of:

1. Midbrain

2. Pons

3. Medulla oblongata

It connects the brain to the spinal cord.

What are the functions of the brainstem?

• sends and coordinates messages between the brain and body

• regulates respiratory systems

• regulates cardiovascular systems

• controls consciousness

• controls alertness

• helps control pain.

Where is the hypothalamus located?

The hypothalamus is located deep within the brain.

What is the main function of the hypothalamus?

The hypothalamus links the:

nervous system → endocrine system

It receives messages from neurones and helps maintain homeostasis.

Which body functions does the hypothalamus help regulate?

The hypothalamus controls:

• body temperature

• blood pressure

• water levels

• blood glucose levels.

It often does this by sending messages to the pituitary gland to release hormones.

Where is the pituitary gland located?

• is located at the base of the brain

• is connected to the hypothalamus

• is approximately pea-sized.

Why is the pituitary gland called the “master gland”?

The pituitary gland is called the master gland because it controls the actions of other glands in the endocrine system.

What are the three lobes of the pituitary gland?

• Anterior lobe

• Posterior lobe

• Intermediate lobe

What is the function of the anterior lobe of the pituitary gland?

• produces hormones

• secretes hormones into the bloodstream.

What is the function of the posterior lobe of the pituitary gland?

• stores hormones produced by the hypothalamus

• releases these hormones when needed.

What is the function of the intermediate lobe of the pituitary gland?

The intermediate lobe produces:

Melanocyte-stimulating hormone (MSH)

MSH regulates pigment production in:

• skin

• hair.

What are the meninges?

The meninges are protective membranes that cover:

• the brain

• spinal cord.

What are the three layers of the meninges?

From outermost to innermost:

1. DuPia mater (inner layer)

2. Arachnoid mater (middle layer)

3. Dura mater (outer layer)

What are the functions of the meninges?

• protect the brain and spinal cord

• support blood vessels

• support nerves

• support cerebrospinal fluid (CSF)

• support the surrounding lymphatic system.

What is cerebrospinal fluid (CSF)?

• a clear, colourless fluid

• found around the brain and spinal cord.

What are the functions of cerebrospinal fluid (CSF)?

• protects the brain and spinal cord from injury

• transports waste products away from the brain

• helps the CNS function correctly.

What are interneurons (relay neurones)?

Interneurons are neurones found only in the CNS.

Their function is to:

• receive impulses from one neurone

• transmit impulses to another neurone.

What is the pituitary gland and why is it important?

The pituitary gland is a small gland at the base of the brain.

It is called the master gland because it controls other endocrine glands.

What is the function of the hypothalamus?

• Links the nervous system and endocrine system

• Maintains homeostasis

• Controls temperature, blood pressure, water levels and blood glucose

What are neurones?

Neurones are specialised nerve cells that transmit electrical impulses around the body.

What are the three types of neurones?

1. Sensory neurones

2. Motor neurones

3. Interneurons (relay neurones)

What is the function of motor neurones?

Motor neurones carry impulses from the CNS to muscles and organs, causing a response.

What is the function of sensory neurones?

Sensory neurones carry impulses from sensory receptors to the CNS.

Where are interneurons (relay neurones) found?

Interneurons are only found in the central nervous system.

What is the function of interneurons?

Interneurons receive impulses from one neurone and transmit them to another neurone.

What are dendrites?

Dendrites are finger-like projections extending from the cell body that receive impulses from other nerve cells.

What is the soma (cell body)?

The soma contains the nucleus and produces substances needed for the neurone to function.

What is the function of the nucleus in the soma?

The nucleus controls the activities of the neurone and produces RNA needed for energy production.

What are axons?

Axons are long extensions from the soma that carry nerve impulses away from the cell body towards another neurone or target tissue.

Why are axons longer than dendrites?

Axons need to carry impulses over longer distances to other neurones, muscles or organs.

What are Schwann cells?

Schwann cells form the myelin sheath around axons.

What is the function of the myelin sheath?

• Insulates the axon

• Allows nerve impulses to travel faster

How is the myelin sheath similar to electrical cables?

Like plastic coating around electrical wires, the myelin sheath insulates and protects the nerve fibre.

What are nodes of Ranvier?

Nodes of Ranvier are gaps between Schwann cells where the myelin sheath is missing.

What is the function of nodes of Ranvier?

They allow the nerve impulse to jump between gaps, increasing the speed of transmission.

What are synaptic knobs?

Synaptic knobs are bulb-shaped endings at the end of an axon where neurotransmitters are stored.

What is an action potential?

An action potential is an electrical nerve impulse generated by neurones that travels along the neurone to transmit information.

What happens when an action potential reaches the end of a neurone?

The action potential reaches the synaptic knob, causing neurotransmitters to be released into the synapse.

What is a synapse?

A synapse is the junction or gap between two neurones where impulses are transmitted.

Why can electrical impulses not directly cross the synaptic gap?

Because there is a physical gap between neurones, so chemical neurotransmitters are needed to carry the signal across.

What are neurotransmitters?

Neurotransmitters are chemical messengers that allow nerve impulses to cross the synaptic gap between neurones.

Describe how an impulse crosses a synapse.

1. An action potential reaches the synaptic knob.

2. Neurotransmitters are released.

3. Neurotransmitters diffuse across the synaptic gap.

4. They bind to receptors on the next neurone.

5. A new electrical impulse is generated.

What are receptors in a synapse?

Receptors are proteins on the membrane of the receiving neurone that bind to neurotransmitters.

What can neurotransmitters cause in target tissues?

• Stimulate activity

• Inhibit activity

• Modify activity

Explain the pathway of information in a reflex arc. (6 marks)

1. A stimulus is detected by a receptor.

2. A sensory neurone carries the impulse to the spinal cord.

3. The relay neurone connects the sensory and motor neurones.

4. The motor neurone carries the impulse away from the CNS.

5. The effector muscle contracts.

6. A rapid response occurs to protect the body.

Explain the importance of the myelin sheath. (3 marks)

The myelin sheath:

• Insulates the axon.

• Prevents loss of electrical signals.

• Allows impulses to travel faster.

Explain why synapses are important. (3 marks)

Synapses allow communication between neurones by:

• Releasing neurotransmitters.

• Passing impulses between cells.

• Ensuring signals travel in the correct direction.

What is homeostasis?

Homeostasis is the process by which the body maintains a stable internal environment so cells can function effectively despite changes inside or outside the body.

Why is homeostasis important?

Homeostasis is important because cells require stable conditions to function properly. If conditions change too much, body processes can slow down or stop, causing illness.

What variables are controlled by homeostatic mechanisms?

The main variables controlled are:

• Blood glucose levels

• Body temperature

• Water levels

What is a negative feedback mechanism?

A negative feedback mechanism is a control system that reverses a change in the body to restore normal conditions (the status quo).

What is the purpose of negative feedback?

Its purpose is to prevent a variable moving too far from its normal range and maintain stability.

What is the first stage of a negative feedback mechanism?

A change occurs in the internal or external environment.

Example:

• Body temperature rises.

What detects changes in the body during homeostasis?

Receptors detect changes.

Example:

• Temperature receptors detect changes in body temperature.

What happens after receptors detect a change?

Nerve impulses are sent to the control centre.

Where is the control centre usually located?

What does the control centre do?

The control centre processes information and sends signals to effectors to correct the change.

What are effectors?

Effectors are organs or tissues that produce a response to restore balance.

Examples:

• Muscles

• Glands

What is the final stage of a negative feedback mechanism?

A response occurs that counteracts the original change, returning the body to normal conditions.

Why must blood glucose levels be controlled?

Cells need a constant supply of glucose for cellular respiration and energy production.

What is the normal fasting blood glucose range?

4.0–5.4 mmol/L.

What is the normal blood glucose level up to two hours after eating?

Up to 7.8 mmol/L.

What causes blood glucose levels to rise?

Eating carbohydrates causes them to be broken down into glucose, which enters the bloodstream.

Which organ detects rising blood glucose levels?

The pancreas.

Which cells in the pancreas detect rising blood glucose?

Beta cells in the Islets of Langerhans.

Which hormone is released when blood glucose levels rise?

Insulin

How does insulin reduce blood glucose levels?

• Allows glucose to enter body cells for cellular respiration.

• Converts excess glucose into glycogen for storage in the liver and skeletal muscles.

What happens when blood glucose levels return to normal?

Insulin production decreases, stopping the mechanism.

What happens when blood glucose levels fall?

The pancreas releases glucagon to increase blood glucose levels.

Which cells produce glucagon?

Alpha cells in the Islets of Langerhans.

How does glucagon increase blood glucose levels?

Glucagon converts stored glycogen in the liver into glucose, which enters the bloodstream.

How are insulin and glucagon different?

Insulin	Glucagon
Lowers blood glucose	Raises blood glucose
Released by beta cells	Released by alpha cells
Converts glucose → glycogen	Converts glycogen → glucose

What is adrenaline?

Adrenaline is a hormone released by the adrenal medulla during the fight or flight response.