Nervous System Exam Notes

The Nervous System

  • Responsible for coordination, response to stimuli, intelligence, thought, self-awareness, and emotion.
  • Two major divisions:
    • Central Nervous System (CNS): Brain and spinal cord; the body's control center.
    • Peripheral Nervous System (PNS): Rest of the nervous system; somatic (voluntary) and autonomic (automatic).

Neurons

  • Nerve cells with three parts:
    • Dendrites: Receive information.
    • Cell Body: Contains the nucleus.
    • Axon: Sends impulses away from the cell body.
  • Types of neurons:
    • Sensory: From sense organs to the CNS; long dendrite and short axon.
    • Motor: From the CNS to muscles or glands; short dendrites and long axon.
    • Interneurons: Found within the CNS between sensory and motor neurons.
  • Myelin Sheath: Fatty coating covering many axons (and some dendrites). Spaces are called Nodes of Ranvier.

Reflex Arc

  • Automatic, involuntary responses.
    • Receptor: Generates the nerve impulse.
    • Sensory Neuron: Transmits the message to the CNS.
    • Interneuron: Passes the impulse to a motor neuron.
    • Motor Neuron: Takes the message from the CNS to the effector.
    • Effector: Muscle or gland that reacts.

Nerve Impulse

  • Neuron transmits information via nerve impulses.
  • Resting potential: −65mV-65mV (inside negative compared to outside).
  • Sodium-potassium pump maintains unequal ion distribution.
  • Action potential: Rapid polarity change above threshold.

Synapse

  • Transmission across a synapse:
    • Impulse reaches axon bulb.
    • Calcium channels open, \Ca^{2+} enters.
    • Synaptic vesicles fuse with the presynaptic membrane.
    • Neurotransmitters released into the synaptic cleft.
    • Neurotransmitters bind to receptors on the postsynaptic membrane.

Nerves

  • Bundles of neuron fibers wrapped in connective tissue.
  • 12 pairs of cranial nerves attached to the brain (sensory, motor, or mixed).
  • 31 pairs of spinal nerves emerge from the spinal cord.

Peripheral Nervous System

  • Lies outside the CNS; contains cranial and spinal nerves.
    • Somatic system (skeletal muscles, voluntary).
    • Autonomic system (smooth muscle, cardiac, glands, involuntary).
    • Sympathetic NS: "Fight or flight".
    • Parasympathetic NS: Relaxed state.

Neurotransmitters

  • Fast-acting neurotransmitters use gated ion channels.
  • Slower-acting neurotransmitters affect cell metabolism.
  • Examples: Acetylcholine (ACh, relaxing), Norepinephrine (NE, excitatory).
  • Neurotransmitters are removed after the response is initiated (enzymes or reabsorption).

Autonomic Nervous System

  • Controls internal organs automatically.
  • Motor neurons divided into sympathetic and parasympathetic.
    • Sympathetic System: Fight or flight; increases heart rate, dilates bronchi, increases breathing rate and BP; releases norepinephrine.
    • Parasympathetic System: Relaxed system; promotes digestion, slows heart and breathing rate; neurotransmitter is acetylcholine.

Adrenaline

  • Produced by the adrenal medulla in response to sympathetic NS stimulation.
  • Increases heart rate and breathing, dilates blood vessels in vital areas.

Central Nervous System

  • Brain and spinal cord, protected by bone and meninges.

The Brain

  • Cerebrum: Conscious thought, memory, personality.
  • Medulla Oblongata: Autonomic functions; heart rate, breathing rate, BP.
  • Thalamus: Relay station for sensory input.
  • Hypothalamus: Homeostasis, hunger, thirst, body temp; controls the pituitary gland.
  • Cerebellum: Balance and posture, complex muscle movement.
  • Corpus Callosum: Connects brain hemispheres.
  • Pituitary Gland: Master gland; controls reproductive hormones (anterior) and kidney function (posterior).