Chapter 15: Coordination

Question 1

3 types of neurone

Answer 1

• Sensory neurones: transmit impulses from receptors to the CNS
• Intermediate neurones (relay/ connector neurones): transmit impulses from sensory neurones to motor neurones
• Motor neurones: transmit impulses from the CNS to effectors.

Question 2

Nervous system

Answer 2

• brain and spinal cord - central nervous system (CNS)
• the cranial and spinal NERVES - peripheral nervous system (PNS)
• Cranial attached to brain
• Spinal nerves attached to spinal cord

Question 3

Endocrine and Nervous System

Answer 3

• Endocrine system utilize hormones and chemical messengers released from ductless glands to the blood stream.
• These substances bind to the receptors on the cell membranes of the target organs/ cells/ tissues
  E.g: Insulin produced by the pancreas targets the liver, causes it to decrease blood glucose level, by taking in glucose and turning it into glycogen.
• Nervous system utilize action potentials along neurones and synapses, from a receptor, pass a coordinator, to an effector.
• Endocrine has a slow, but more long lasting and widespread effect.

Question 4

Nerve cells

Answer 4

• known as neurones
• Carry info directly to their target cells
• Coordinate the activities of SENSORY RECEPTORS (in the eye), decision-making centres in the CNS, and EFFECTORS ( muscles and glands)

Question 5

Structure and function of motor and sensory neurones

Answer 5

• Motor neurone:
  + Cell body of a motor neurone lies within the spinal cord or brain (CNS).
  + Cytoplasm containing many mitochondria and extensive rough ER
  + Dendrites: short, often branched to give a large surface area for the endings of other neurones
  + Axons: longer -> conducts impulses over long distance, may be to toes.
  + Axon’s cytoplasm has large numbers or mitochondria, together with many vesicles containing chemicals called transmitter substances.
• Sensory neurone:
  + same basic structure, but it has one long axon with a cell body that may be near the source of stimuli/ in a swelling of a spinal nerve (A GANGLION)
• Relay neurone:
  + entirely within the CENTRAL NERVOUS SYSTEM (CNS)

Question 6

Transmitter substance

Answer 6

involved in passing impulses to an effector cell such as a muscle/ gland cell

Question 7

Myelin

Answer 7

• made of Schwann cells wrapping around the axon all along its length
• Schwann cell spirals around, enclosing the axon in many layers of its cell surface membrane.
• > Enclosing sheath = MYELIN SHEATH
• made largely of lipid, with proteins.
• affects the speed of conduction of the nerve impulse.
• not all axons are protected my myelin. 2/3 of motor and sensory neurones are unmyelinated.
• Nodes of Ranvier

Question 8

Nodes of Ranvier

Answer 8

• the small, uncovered areas of axon between Schwann cells
• occur about every 1 - 3 mm in human neurones.
• small, about 2 - 3 um long

Question 9

Spinal Reflex arcs

Answer 9

1. Input from receptor (nerve impulses)
2. Sensory Neurone via DORSAL ROOT of spinal nerve (white matter - mostly axons)
3. Cell body of sensory neurone
4. Cell body of intermediate neurone
5. Cell body of motor neurone
   (grey matter - mostly cell bodies)
6. To motor neurone via VENTRAL ROOT of spinal nerve
7. Output to effector
   - impulse is passed from neurone to neurone inside the spinal cord.
   - may have impulse passes directly from sensory to motor.
   -

Question 10

Reflex arc

Answer 10

the pathway along which impulses are transmitted from a receptor to an effector without involving conscious regions of the brain

Question 11

Reflex action

Answer 11

• The impulse will also be passed on to other neurones which take the impulse up the cord to the brain same time as impulses are travelling along the motor neurone to the effector.
• Effector responds to the stimulus before there is any voluntary response involving conscious region.
• Fast, automatic response to a stimulus, response is always the same to each specific stimulus.
• useful way of responding to danger signals: touch very hot object/ sight of an object flying towards you.

Question 12

Transmission of nerve impulses

Answer 12

• Neurones transmit electrical impulses.
• Travel very rapidly along the cell surface membrane from one end to the other
• The signals are very brief changes in the distribution of electrical charge across the cell surface membrane: ACTION POTENTIALS, caused by the very repid movement of sodium ions and potassium ions into and out of the axon

Question 13

Resting potential

Answer 13

• inside the axon always has a slightly negative electrical potential compared with the outside (-60 mV to -70mV)
• produced and maintained by the sodium-potassium pumps in the cell surface membrane. use energy from the hydrolysis of ATP.
• ## 3 sodium ions are removed from axon for every 2 potassium ions brought in.