nervous system

What is a neurotransmitter

Chemicals which carry impulses across the synapse

What is Alzheimer’s disease

A disease caused by nerve defects, usually in older people, and characterized by memory loss and confusion

What is multiple sclerosis

A disease caused by damage to the myelin sheath of neurons and characterized by physical and mental disabilities.

What is grey matter?

A part of the brain and spinal cord consisting of myelinated axons.

What is a synapse?

: A gap between the axon of one neuron and the dendrites of another neuron.

What do the central and peripheral nervous systems consist of?

CNS: brain and spinal cord.
PNS: cranial nerves and spinal nerves.

How is the brain protected?

The cranium and meninges protect the brain, and it is cushioned by cerebrospinal fluid.

What are the functions of the cerebrum?

A: Controls voluntary actions; receives and interprets sensations; controls higher thought processes such as memory and intelligence; allows communication between the two halves of the brain.

What are the functions of the cerebellum?

Coordinates skeletal muscles for balance when walking and moving; maintains balance, posture and muscle tone.

What are the functions of the medulla oblongata?

A: Controls breathing, peristalsis, heartbeat and swallowing; transmits impulses from the spinal cord to the brain; controls reflexes such as blinking, coughing, sneezing, vasodilation, vasoconstriction and salivating.

What is the hypothalamus and what does it control?

A section of the brain just above the pituitary. It is a control centre for hunger, thirst, sleep, body temperature and emotions.

How is the spinal cord structured?

The spinal cord has 33 vertebrae with discs of cartilage between them to act as shock absorbers.

How is the spinal cord protected?

A: By the vertebrae, meninges and cerebrospinal fluid.

Where does the spinal cord extend?

A: From the medulla oblongata to the lumbar region in the lower back.

What are the functions of the spinal cord?

A: Transmits impulses from receptors to the brain and from the brain to the effectors, and contains reflex centres that function automatically to protect the body.

What are neurons?

Specialized cells which connect the brain and spinal cord to all other parts of the body.

What is the function of dendrites?

Transmit impulses towards the cell body.

Cell body

A: Contains the nucleus, which controls the metabolism of the cell.

Q: What is the function of an axon?

Transmits impulses away from the cell body.

What are the functions of the myelin sheath and neurilemma?

The myelin sheath insulates the axon and speeds up the transmission of impulses. The neurilemma helps repair damaged neurons.

What are the three types of neurons?

: Sensory neurons, interneurons and motor neurons.

What is the function of a sensory neuron?

Transmits impulses from the receptor to the central nervous system.

What is the function of an interneuron?

A: Connects a sensory neuron to a motor neuron in the central nervous system.

What is the function of a motor neuron?

A: Transmits impulses from the central nervous system to the effectors, which are muscles and glands.

Q: What is the significance of a synapse?
A:

• Ensures that the impulse moves in one direction only.

• Prevents continuous stimulation of neurons.

• Ensures that the impulse is transmitted from the sensory neuron to the motor neuron.

What are a reflex action and a reflex arc?

Reflex action: a quick, automatic response to a stimulus.
Reflex arc: the pathway along which an impulse is transmitted to bring about a response to a stimulus during a reflex action.

What is the significance of a reflex action?

A: Allows for a quick response without thinking about it, helping to prevent damage to the body.

Reflex arc — process
Q: Describe the reflex arc process.
A:

1. Stimulus is detected by receptor cells.

2. Receptors convert the stimulus into a nerve impulse.

3. The impulse travels along the sensory neuron through the dorsal root to the spinal cord.

4. The sensory neuron transmits the impulse to an interneuron.

5. The interneuron transmits the impulse to a motor neuron.

6. The impulse exits the spinal cord through the ventral root.

7. The motor neuron transmits the impulse to the effector.

8. The effector reacts appropriately.

Why does a reflex action occur before the brain processes the sensation?

A: The reflex arc is completed through the spinal cord before the impulse reaches the brain, allowing a rapid response. The brain receives the impulse afterwards, when the sensation of pain is felt.

Where are the receptor cells of the eye found, and what are they?

Receptor cells are found in the retina. The two types are rods and cones.

What are the functions of rods and cones?

• Rods: sensitive to dim/low-intensity light; provide black-and-white vision, night vision and peripheral vision.

• Cones: sensitive to bright light; provide sharp, clear colour vision.

What are the pupillary mechanism and accommodation?

• Pupillary mechanism: regulation of pupil size to control the amount of light entering the eye.

• Accommodation: ability of the lens to alter its shape for clear vision when viewing near and distant objects.

What do convex and concave mean?

• Convex: curves outwards; thicker in the middle than at the edges.

• Concave: curves inwards; thinner in the middle than at the edges.

What are binocular and stereoscopic vision?

• Binocular vision: using two eyes with overlapping fields of view so separate images are combined and interpreted as one image by the brain.

• Stereoscopic vision: ability to form three-dimensional images, allowing distance, depth and size of an object to be judged.

What is the function and adaptation of the sclera?

Function: protects the inner structures of the eye and maintains its shape.
Adaptation: tough, white and inelastic layer covering the eye towards the posterior, providing protection.

The cornea is a transparent continuation of the sclera.

• Its transparency allows light to pass through.

• Its convex shape causes refraction, bending incoming light to create an image on the retina.

Q: What is refraction?

The bending of incoming light to create an image on the retina.

What are the functions and adaptations of the choroid?

• Pigments absorb light and prevent reflection inside the eye.

• Blood vessels supply nutrients and oxygen to the cells of the retina.

Q: What is the function of the ciliary body?

Contains ciliary muscles, which contract or relax to alter the tension on the suspensory ligaments during accommodation.

What are the functions of the suspensory ligaments?

A: They are attached to the ciliary body and hold the lens in position. Their tension changes to alter the shape of the lens during accommodation.

What is the function and adaptation of the iris?

A: The iris is the coloured portion of the eye with an opening at its centre. It contains two muscles that control pupil size and therefore the amount of light entering the eye.

What are the functions and adaptations of the retina?

What are the functions and adaptations of the retina?

The retina is the inner layer of the eye and contains rods and cones sensitive to light. Neurons from the retina carry impulses from the rods and cones to the optic nerve and then to the cerebrum.

Q: What do rods do?

A: Respond to low-intensity light and provide night vision and peripheral vision.

What do cones do?

A: Respond to bright light and provide sharp, clear colour vision.

What are the yellow spot and blind spot?

• Yellow spot: area of clearest vision.

• Blind spot: area of no vision.

What are the functions and adaptations of the lens?

The lens changes shape to focus on near and distant objects. It is a transparent, elastic, biconvex structure behind the pupil, held in place by suspensory ligaments. Its transparency allows light to pass through.

What is the function of the aqueous humour?

Watery fluid between the cornea and lens that maintains the shape of the cornea and plays a small role in the refraction of incoming light.

What is the function of the vitreous humour?

A: Jelly-like substance behind the lens that maintains the shape of the eyeball.

Describe accommodation for near vision.

1. Ciliary muscles contract.

2. Suspensory ligaments slacken.

3. Tension on the lens decreases.

4. Lens becomes more convex.

5. Light bends more.

6. A clear image is focused on the retina.

Describe accommodation for distant vision.

1. Ciliary muscles relax.

2. Suspensory ligaments tighten.

3. Tension on the lens increases.

4. Lens becomes less convex.

5. Light bends less.

6. A clear image is focused on the retina.