System Neurobiology

Organization of the nervous systems

Major divisions of the vertebrate nervous system

central nervous system

  • Brain

    • higher function

    • complex task initiation

    • perception

    • emotions

  • Spinal cord

    • reflexes

    • carries sensory and motor signals

  • Protected by meninges and cerebrospinal fluid (CSF)

    • Meninges

      • Dura mater

        • tough matter

        • outermost

      • Arachnoid matter

        • weblike

        • middle layer

      • Pia mater

        • delicate matter

        • thin

        • inner layer

  • Blood brain barrier

    • prevents the wrong molecules from going to the brain

    • prevents glucose

    • does not prevent fats

    • White matter

      • myelinated

      • Brain: in the inner part

      • Spinal cord: on the outside

    • Gray matter

      • unmyelinated

      • Brain: on the outside

      • Spinal cord: on the inside

Functions of the spinal cord

  • mediates spinal reflexes

  • pathway for impulses to and from the brain

Axons of the peripheral neurons bundles into nerves

  • Nerve- a collection of nerve fibers in the PNS-connect sensory organs to CNS. May or may not be myelinated

  • Tract- collection of nerve fibers in the CNS (usually myelinated-white matter)

  • Peripheral neuron cell bodies cluster in or near the CNS

  • if neuron cell bodies are clustered in the CNS- nuclei

  • if neuron cells are clustered outside the CNS- ganglia

  • Nerves may contain sensory pr motor signals or both

Reflex arc control many involuntary behaviors

  • automatic, subconscious response to stimuli within or outside the body

    • simple reflex arc(sensory-motor)

    • most common (sensory -assoication-motor)

Simple reflex arc involve only 2 neurons

Most reflexes are mediated by more neurons

  • a withdrawal reflex involves a sensory neuron, an interneuron, and a motor neuron

Reflex arcs employ divergence to ensure coordinated responses

Bundles of axons in the CNS are called tracts

  • Different information carried in ascending and descending tracts

Efferent outputs

  • originate in the brain

    • ipsilateral

      • same side

    • contralateral

      • opposite side

      • mostly muscle neurons

    • Sorting sensory inputs in the brain

      • Touch

        • contralateral

      • Hearing

        • both

      • eyesight

        • both

3 fundamental division of the vertebrate brain

  • Hindbrain

    • reflexes and involuntary behavior

    • metencephelon and myelencephalon

    • medulla oblongata

      • breathing, heart rate, blood pressure

    • pons

    • cerebellum

      • motor behaviors

  • midbrain

    • mesencephalon

  • forebrain

    • telencephelon and diencephalon

    • Frontal

      • primary motor cortex

        • controls voluntary movements in skeletal muscle

        • stimulation of different regions f PMC leads to movement

        • Damage to the PMC leads to paralysis and loss of voluntary movement

        • damage to the PMC usually results in permanent loss of these movements

      • pre motor cortex

        • coordinates movements of groups of muscles

        • damage:

          • loss of skill

          • can be relearned

    • parietal

      • primary somatosensory cortex

        • behind the central sulcis

        • primary input from sensory receptors in skin and muscle

        • damage leads to loss of sensation

      • somatosensory association area

        • adjacent to primary somatosensory cortex

        • interpretation of sensation

        • integration sensation with memory

        • damage: loss of identification of sensations

    • temporal

    • occipital

      • primary visual cortex

        • message goes to the cortex

      • visual association area

        • interepreting the message

Homunculus

  • motor

  • sensory

Autonomic nervous system

  • 3 branches

    • sympathetic

      • most active during stress excitement, or physical activity

      • fight or flight

      • increases HR, breathing rate, directs blood to working muscles

    • parasympathetic

      • most active during rest

      • resting and digesting

      • redirects energy toward maintenance activated like digestion

    • enteric

    • Effector organs express different metabotropic adrenergic receptors

    • Most organs have dual innervation from the parasympathetic and sympathetic branches

How can sympathetic input alone control dilation and constriction?

The adrenal medulla is innervated by the sympathetic nervous system only

The CNS regulates both voluntary and involuntary efferent branches

  • somatic motor neurons innervate skeletal muscle for voluntary movements

Vertebrate motor neurons release ACh at the neuromuscular junction

  • Acetylcholine (ACh)

    • released from synaptic vesicles

    • binds to nicotinic ACh receptors

    • causes skeletal muscle depolarization via entry of sodium ions into the cell