Neurons, nerves, synapses,reflex arc

Question 1

Give the three classifications/types for neurons

Answer 1

*Sensory/unipolar neurons

-Afferent neurons as they carry impulses from receptors towards the CNS where the sensation is interpreted.
af = towards
unipolar = one fibre attached to the cell body

*Connector neurons AKA relay neurons, association neurons or interneurons

-These are multipolar neurons found in the CNS and make up 99% of the neurons of the body.
Receive impulses from sensory neurons and pass them on to other neurons.

*Motor/multipolar neurons

-These are efferent neurons as they carry impulses away from the CNS to effectors so that the appropriate response can be brought about.
ef = away from

Question 2

Explain the fibres of a neuron

Answer 2

Fibres in a typical neuron are:

× Dendrites that conduct impulses towards the cell body. They branch extensively to provide a large surface area to receive signals from other neurons.

× Axon conducts impulses away from the cell body. Each neuron has a single axon although certain axons may give off branches along their length. An axon usually branches extensively at its end to form terminal branches.

Question 3

Neuroglia

Answer 3

Supporting cell, that plays a role in making myelin and supporting and protecting the neurons.

Question 4

What is a nerve?

Answer 4

The basic unit of the nervous system is anerve cell or neuron. Bundles of neurons are callednervesin the PNS andtractsin the CNS.

Question 5

Explain the structure of a nerve (3)

Answer 5

The neurons are bound together intobundlesby connective tissue called theperineurium.

Inside the bundles the neurons are surrounded by delicate connective tissue called theendoneurium.

The entire nerve is surrounded by a sheath of connective tissue, theepineurium.

An artery and a vein occur between the bundles, to nourish the fibres and remove waste.

Question 6

What is the function of a nerve?

Answer 6

Nerves carry impulses from receptors to the CNS and from the CNS to effectors to bring about appropriate responses.

Question 7

What is a nerve impulse

Answer 7

An electrical signal that travels along a nerve fiber in response to a stimulus

Question 8

How are nerve impulses transmitted?

Answer 8

1. Resting potential:
   ➡️Diff. in CHARGE across the cell membrane.

•Neuron not stimulated + Membrane is POLORIZED () = Resting state

2.Active potential:
➡️Conduction of NI along neuron in response to a stimulus

•Neuron is stimulated = Results in depolarisation; inside of cell is ➕
and outside is ➖

•If stimulus = strong enough (above certain threshold potential) THEN complete depolarisation results in: BURST of electrical activity, passing along neuron as NI.
(All or nothing response: Threshold potential not reached = NO NI generated).

3.Refractory potential:
➡️Recovery stage = Membrane is repolarized when impulses pass along.

•Cause of this?: Carrier molecules actively transporting the IONS back through membrane to their OG position

Question 9

What is Synapses?

Answer 9

➡️The junction across which a nerve impulse passes from an axon terminal TO a neuron, muscle cell or gland cell.

Question 10

How do impulses travel across synapses?

Answer 10

NI reach terminal branches of axons
⬇️
Cause vesicles in pre-synaptic knob to BURST
⬇️
This releases neurotransmitters
⬇️
They diffuse across the synaptic gap
⬇️
They then carry impulses across gap (Chemical Process)
⬇️
This stimulates receptors in post- synaptic membrane to initiate NI

Question 11

Why is Synapses important?

Answer 11

ENSURE impulses FLOW in 1D, cause vesicles containing transmitters = only in axon terminal knobs ∵ impulses = only transmitted from 1 side.

ALLOW FILTERING OUT of continual and unnecessary stimuli, cause if neuron is constantly transmitted synapse can’t renew supply of transmitters fast enough to continue passing the impulse across the cleft.

Question 12

What is a reflex arc?

Answer 12

↳ PATHWAY followed by impulses from receptor to effector to bring a reflex action.

Question 13

What are the types of reflex centres (2)?

Answer 13

*Stomatic – skeletal
*Autonomic – Smooth/cardiac muscles and glands

Question 14

Where are reflex centres activated (2)?

Answer 14

➤Brain
➤Spinal Cord_ primitive reflexes

Question 15

What is the importance of a reflex arc?

Answer 15

✔️ENABLES body to respond QUICKLY to stimulus.
✔️PROVIDES inborn SAFETY MECHANISMS serving to protect body from danger.

Question 16

What happens if a person touches a hot stove? Explain reflex action in full.

Answer 16

The receptor detects stimuli THEN impulses are then generated.
Impulses are sent along SENSORY neuron to CNS THEN to the connector neuron
THEN to the motor neuron THEN to effector neuron which produces a response i.e., Hand moves away.