Human Biology 2 Exam Revision - Week 1

Nervous system, action potentials, and neurotransmitters

Central Nervous System (CNS)

Brain and spinal cord, understands sensory information, and makes decisions

Peripheral Nervous System (PNS)

Everything else, Commands from CNS → body, message transport system

How does the NS maintain body homeostasis in response to detected changes?

Stimulus → receptor → control centre → effector → negative feedback -

The nervous system controls body organ systems to react to changes internal and external

Sensory nervous system (afferent)

Carries nerve impulses from receptors to the CNS

Motor nervous system (efferent)

Carries nerve impulses from CNS to effectors

Somatic division (voluntary)

Conducts impulses from CNS to skeletal muscles

Autonomic division (involuntary)

Conducts impulses from CNS to cardiac, smooth muscles, and glands

Sympathetic nervous system

• Mobilises body systems to prepare for/during activity

• Using energy to move

• “Fight or flight”

Parasympathetic nervous system

• Conserves energy

• Rests body functions

• “Rest and digest”

Features of a neuron

1. Dendrites

2. Cell body

3. Nucleus

4. Axon

5. Axon terminal

6. Myelin sheath

7. Nodes of ranvier

Neurotransmission

Chemical messages from neuron to neuron to send body cells signals

Action potentials

Electrical messages that travel down a neuron’s axon

Features of neurons in neurotransmission

1. Neurotransmitter attaches to receptors on axon terminal

2. Triggers short muscle contraction

3. Chemical message neurons used to send signals to the body cells

4. Via. Endo/exco cytosis

Features of neurons in action potentials

• Stimulus may produce an action potential

• Slower signal but utilises all functions of the neuron

Electrical (rare) synapse

Cells link by physical direct contact

Chemical (common) synapse

Utilises synapse and neurotransmission

Active transport

• Requires ATP energy)

• Moves solutes against the concentration gradient (low → high)

• Utilises help from carrier proteins

• Cell has more Na+ on outside, and more K+ inside

Potential difference

• Positive and negative electrical charges are held apart

• Potential difference = membrane potential

• Resting membrane potential = -70mV

Neuron membrane potentials

• Changes due to temporary changes in membrane permeability

• Results from opening and closing of specific membrane channels

Passive membrane channels

• Leak passages

• No ATP energy required

What electrolytes are required for different stages in action potentials?

1. Resting state (-7mV) → Sodium (Na+) and Potassium (K+)

2. Depolarisation (rising phase) → Sodium (Na+) enters the cell

3. Repolarization (falling state) → Potassium (K+) rushes out the cell

4. Hypolarization (refractory period) → Potassium (K+) excess K+ leaks out

What are the glial cells of the CNS and their functions?

1. Astrocytes → Blood brain barrier

2. Ependymal cells → Fluid lining brain and spinal cord

3. Oligodendrocytes → Myelin

What are the glial cells in PNS and their functions?

1. Schwann cells → Myelin

2. Satellite cells → Protection of neurons