Week 3 Bioscience

Question 1

Functions of the Nervous System

Answer 1

1. Sensory function
   
   • receptors detect sensory input
   • sensory input is sent to control centre
2. Integrative function
   
   • analyses & interprets sensory input
   • determines appropriate responses
   • generates the motor output that causes the response
3. Motor function - issues motor output to activate an effector

Question 2

General sensory receptors

Answer 2

· Are located in the skin, skeletal muscles, tendons, joints & visceral organs and include:
- thermoreceptors - detect changes in temperature
- nociceptors - detect painful stimuli
- mechanoreceptors
▪ tactile receptors - detect touch, pressure & vibration stimuli
▪ baroreceptors - detect changes in blood pressure
proprioceptors - detect changes in body position (proprioception)

Question 3

Special sensory receptors

Answer 3

· Are located in the eyes, ears, mouth & nose and include:
- photoreceptors - detect light (vision)
- chemoreceptors - detect chemicals in solution (taste & smell)
- mechanoreceptors called hair cells - detect hearing & balance stimuli

Question 4

CNS

Answer 4

· Consists of the brain and spinal cord
· Control centre - performs the function of integration
· Controls our emotions, behaviours and personality
· Performs intellectual (cognitive) functions § Stores memories

Question 5

PNS

Answer 5

· Consists of sensory receptors and the cranial, spinal and peripheral nerves that link all parts of the body to the CNS
- cranial nerves and their branches primarily innervate structures of the head & neck
- spinal nerves branch to form the peripheral nerves that innervate all parts of the body below the head

Question 6

Somatic Nervous System

Answer 6

· Conveys “somatic” motor output from the CNS to the body’s skeletal muscles
· Somatic motor output controls:
- voluntary skeletal muscle movements
- involuntary skeletal muscle movements = somatic reflexes

Question 7

Autonomic Nervous System

Answer 7

· Conveys “autonomic” motor output from the CNS to the body’s glands, cardiac & smooth muscles
· Autonomic motor output controls involuntary (automatic) activities, e.g.
- heart rate
- respiration (respiratory airflow)
- blood vessel and pupil diameter
- digestion of food
- urination & defecation
- perspiration & salivation

Question 8

Sympathetic division

Answer 8

Controls “fight-or-flight” activities - activates body functions that support physical activity and inhibits those that don’t, e.g.
- increases heart rate, respiratory airflow, blood flow to skeletal muscles & sweat gland activity
- dilates pupils
- inhibits digestive functions
- inhibits urination & defecation

Question 9

Parasympathetic division

Answer 9

Controls “rest and digest” activities - activates body functions that conserve and restore body energy, e.g.
- stimulates digestive functions, urination & defecation
- constricts pupils
- decreases heart rate
- decreases respiratory airflow

Question 10

Neuroglia (“nerve glue”)

Answer 10

• Support neuron development and function
• Six different types of cells which collectively nourish, protect, insulate and structurally support neurons

Question 11

Neurons

Answer 11

· Specialised cells - perform the function of communication
- when stimulated they generate electrical signals called graded potentials and action potentials to conduct sensory and motor information from one part of the body to another
· Require oxygen and glucose for survival
- Are unable to divide and replace themselves if destroyed

Question 12

dendrites

Answer 12

• Short processes
• Are the main receptive (or input) region of a neuron
  
  • act as sensory receptors - detect stimuli
  • receive information from other neurons
• Convert the information they receive into a graded potential which conveys the information towards the cell body

Question 13

cell body

Answer 13

• Contains a nucleus and organelles, e.g., ribosomes to synthesise chemical neurotransmitters
• Receives information from other neurons & converts this information into a graded potential
• Integrates information (graded potentials) and conveys information towards the initial segment (or first part) of the axon

Question 14

axon

Answer 14

• A single process that connects to the cell body at the axon hillock
• Is the conducting region of a neuron
• generates & conducts action potentials to convey information from the initial segment to the axon terminals

Question 15

axon terminal

Answer 15

• Form a synapse with another cell - i.e. a neuron, muscle or gland
• Are the secretory region of a neuron
• contain synaptic vesicles that store and release neurotransmitters - chemicals that carry the information from one neuron to another or to a muscle cell or gland

Question 16

myelin

Answer 16

• produced by Schwann cells and oligodendrocytes
• increases the speed of signal conduction
• segments are separated by gaps called nodes of Ranvier (internodes)
• destruction of myelin (oligodendrocytes) in the CNS - multiple sclerosis

Question 17

Sensory Neurons

Answer 17

• Conduct sensory input from receptors to the CNS
• Unipolar in structure

Question 18

Interneurons

Answer 18

• Conduct information within the CNS
• Multipolar in structure

Question 19

Motor Neurons

Answer 19

• Conduct motor output away from the CNS to a muscle or gland
• lower motor neurons conduct somatic motor output
• preganglionic & postganglionic neurons conduct autonomic motor output
• Multipolar in structure

Question 20

Chemically-gated Channels

Answer 20

• Open in response to a chemical stimulus e.g. neurotransmitters
• Located along the plasma membrane of the dendrites & cell body

Question 21

Voltage-gated Channels

Answer 21

• Open and close in response to voltage changes (i.e. changes in membrane potential)
• Located along the plasma membrane of the axon and axon terminals

Question 22

Mechanically-gated Channels

Answer 22

• Open in response to mechanical stimulation e.g. touch, vibration and pressure
• Located along the plasma membrane of the dendrites

Question 23

Changes in membrane potential (voltage)

Answer 23

• Occur when a stimulus opens Na+ or K+ gated channels
• Are relative to the resting membrane potential = -70 mV
• Are described by terms depolarisation & hyperpolarisation

Question 24

Depolarisation = membrane potential becomes less negative

Answer 24

When a stimulus opens Na+ gated channels:
- influx of Na+ ions into the ICF
- ICF gains +ve ions à cell interior becomes less negative
- membrane potential becomes less negative e.g. -70 mV to -60 mV

Question 25

Hyperpolarisation = membrane potential becomes more negative

Answer 25

When a stimulus opens K+ gated channels:
- efflux of K+ ions out of the ICF
- ICF looses +ve ions à cell interior becomes more negative
- membrane potential becomes more negative e.g. -70 mV to -80 mV

Question 26

Graded Potentials (GP)

Answer 26

• Are small changes in the membrane potential (i.e., a small depolarisation or hyperpolarisation)
• Originate in the dendrites or cell body of a neuron, when a stimulus opens chemically-gated or mechanically-gated channels
• Are short distance signals
• distance travelled is proportional to stimulus strength
  stronger stimulus = bigger change in membrane potential = further signal will travel

Question 27

Action Potentials (AP)

Answer 27

• Are long distance signals
• Originate at the initial segment of an axon
• Involve voltage-gated channels
• Are self-propagating

Question 28

Chemical Synapse

Answer 28

• A junction that mediates the transfer of information
• At a chemical synapse between two neurons:
• the neuron sending the information = presynaptic neuron
• the neuron receiving the information = postsynaptic neuron
• presynaptic and postsynaptic membranes are separated by a synaptic cleft
• signal transmission involves chemical neurotransmitters

Question 29

Termination of Synaptic Transmission

Answer 29

1. The neurotransmitter diffuses away from the synaptic cleft
2. The neurotransmitter is degraded by enzymes present in the synaptic cleft
3. The neurotransmitter re-enters the axon terminal and destroyed by enzymes or reused. This process is known as reuptake.