Structure+Function of Nervous System Notes

Nervous System Overview

  • CNS (Central Nervous System): Comprises the brain and spinal cord.

  • PNS (Peripheral Nervous System): Includes nerves connecting CNS to the rest of the body.

    • Afferent Nerves: Transmit information towards the CNS.

    • Efferent Nerves: Transmit information away from the CNS.

Systems Within the Nervous System

  • Sensory Systems:

    • Sight

    • Hearing

    • Smell (Olfaction)

    • Taste (Gustatory)

  • Balance

  • Somatic System:

    • Somatosensory + motor systems

  • Autonomic System:

    • Sympathetic

    • Parasympathetic

Neurons: Primary Communicating Cells

  • Neurons do not divide and are considered highly polarized.

  • Structure of Neurons:

    • Dendrites: Receive information.

    • Axon: Sends information.

    • Cell Body (Soma): Contains the nucleus.

    • Axon Terminals: Release neurotransmitters for communication.

    • Mitochondria: Provide energy.

    • Schwann Cell: Insulate axons; contain myelin sheath.

Glial Cells: Support Cells

  • More numerous than neurons in nervous tissue.

CNS Glial Cells:

  • Astrocytes: Support neurons, provide nutrients, contribute to blood-brain barrier.

  • Oligodendrocytes: Produce myelin sheaths around axons in CNS.

  • Microglia: Clean up debris and infections.

  • Ependymal Cells: Produce cerebrospinal fluid (CSF).

PNS Glial Cells:

  • Schwann Cells: Produce myelin and wrap axons.

  • Satellite Cells: Support neuronal cell bodies in ganglia.

Nervous System Response to Injury

  • Wallerian Degeneration:

    • Occurs when an axon is damaged.

    • Distal axon degrades and undergoes chromatolysis (change in cell body).

  • Schwann Cells proliferate and facilitate regeneration if the lesion is not too large (only in the PNS).

Stages in Nerve Injury Recovery:

  1. Chromatolysis + Nuclear Movement

  2. Distal Axon Degeneration

  3. Sprouting and Axon Regeneration

Nerve Impulse and Neurocommunication

  • An impulse changes resting membrane potential (electrical), transmitting messages via electrical signals.

  • Action Potential occurs in postsynaptic cells if signal reaches a certain threshold.

  • Neurotransmitters: Chemicals released from axon terminals to facilitate communication.

    • Common Types:

      1. Monoamines

      2. Amino Acids

      3. Acetylcholine

      4. Neuropeptides

      5. Nucleotides

  • Postsynaptic Potentials:

    • EPSP (Excitatory): Depolarization that increases likelihood of firing.

    • IPSP (Inhibitory): Hyperpolarization that decreases likelihood of firing.

Brain Structure Overview

1. Forebrain (CNS)

  • Controls thinking and movement:

    • Telencephalon (cerebrum)

    • Diencephalon (thalamus)

2. Midbrain

  • Controls movement and reflexes.

  • Comprises structures like the brain stem.

3. Hindbrain

  • Involved in balance and coordination:

    • Metencephalon (cerebellum + pons)

    • Myelencephalon (medulla oblongata)

Key Brain Structures

  • Frontal Lobe:

    • Contains prefrontal cortex (planning), motor cortex, and Broca's area (speech).

  • Parietal Lobe:

    • Processes somatosensory information, associated with problem-solving and contains Wernicke's area (speech).

  • Occipital Lobe:

    • Primary visual cortex, processes visual information (damage leads to vision problems).

  • Temporal Lobe:

    • Comprises primary auditory cortex, auditory association cortex, processes olfactory information.

  • Insular Lobe:

    • Deep in lateral sulcus; processes sensory and emotional information and regulates mood and feeding behaviors.

Diencephalon Structuring

  • Contains structures such as the thalamus, hypothalamus, and the epithalamus (pineal gland).

  • Interthalamic adhesion is a notable feature connecting both sides of the thalamus.

Spinal Cord and Pathways

  • Cervical (8), Thoracic (12), Lumbar (5), Sacral (5), Coccygeal (1)

  • Spinal Reflexes: Automatic movements in response to sensory stimuli.

Motor Pathways (Spinal Tracts):

  1. Corticospinal (movement)

  2. Rubrospinal

  3. Reticulospinal

  4. Vestibulospinal

  5. Corticobulbar

Sensory Pathways (Spinal Tracts):

  1. Spinothalamic Tract (pain + temperature)

  2. Posterior (Dorsal) Column (discriminative touch)

Protection of the CNS

  • Bone: Skull and vertebrae act as tough coverings.

  • Meninges: Protect tissues, consisting of dura mater (thick), arachnoid mater, and pia mater (innermost).

Blood Supply to the Brain and Spinal Cord

  • Carotid Artery: Supplies blood to the brain

  • Circle of Willis: Features major arteries providing blood to specific brain lobes.

Peripheral Nervous System (PNS)

  • Composed of nerves that are not encased in bone (except brain and spinal cord).

  • Comprised of 12 cranial nerves and 31 spinal nerves, responsible for sensory, motor, and autonomic functions.

Autonomic Nervous System (ANS)

  • Maintains body homeostasis through:

    • Parasympathetic (rest and digest)

    • Sympathetic (fight or flight)

Testing the Nervous System

  1. Imaging Techniques:

  • X-rays, CT scans, MRIs, and PET scans to visualize structures.

  1. Measuring Conduction:

  • EEG (electroencephalograms), MEG, and evoked potentials to study electrical activity.

  1. Biochemical Analyses:

  • Testing blood and cerebrospinal fluid (CSF) for genetic markers and other indicators.