Nervous System

Nervous System Part 1 - Overview

Functions of the Nervous System

  • Sensory:

    • Detects changes in the environment

    • Internal changes: carbon dioxide levels.

    • External changes: temperature of the surroundings.

  • Integration:

    • Processing and decision making

    • Takes sensory information, decides response, and sends to motor side of the nervous system.

  • Motor:

    • Executes the response decision

    • Muscles act in response to sensory input.

Structural Organization of the Nervous System

  • SNS (Somatic Nervous System) and PNS (Peripheral Nervous System) work synergistically:

    • SNS brings sensory information in, processes it, and sends motor signals out.

    • Sensory nerves (afferent): carry information into the spinal cord.

    • Motor nerves (efferent): convey signals away from the spinal cord.

    • Ganglia: cluster of nerves where PNS nerves junction and relay information.

  • Central Nervous System (CNS):

    • Composed of the brain and spinal cord.

  • Peripheral Nervous System (PNS):

    • Composed of cranial nerves, spinal nerves, ganglia, and sensory receptors in skin.

    • Includes enteric plexuses, often referred to as the "brain of the guts."

Nervous System Part 2 - Nerve Types and Structure

Somatic vs Autonomic Nervous Systems

  • Somatic Nervous System:

    • Voluntary control

    • Involves skeletal muscles and senses like touch, pain, and pressure.

  • Autonomic Nervous System:

    • Involuntary control

    • Comprises sympathetic, parasympathetic divisions, and enteric nervous system.

Visceral Sensory Neurons

  • Detect subconscious changes:

    • Blood glucose levels, blood pressure.

Autonomic Motor Neurons

  • Control involuntary actions like:

    • Adjustments to blood pressure, heart rate, hormone secretion.

Neuron Structure

  • The functional unit of the nervous system producing electrical signals:

    • Cell Body: Contains organelles (nucleus, mitochondria).

    • Dendrites: Extensions directing signals towards the cell body.

    • Axon: Carries signals away from cell body to axon terminals.

    • Myelin Sheath: Fatty tissue insulating some axons.

Nervous System Part 3 - Glial Cells

Glial Cells in CNS

  • Astrocytes:

    • Large, regulate blood-neuron interaction, provide structural support.

  • Oligodendrocytes:

    • Create myelin sheaths around axons.

  • Microglial Cells:

    • Respond to pathogens, destroy viruses and bacteria.

  • Ependymal Cells:

    • Line brain/spinal cord cavities, involved in cerebrospinal fluid (CSF) production.

Glial Cells in PNS

  • Satellite Cells:

    • Surround PNS neurons, regulate nutrient and waste exchange.

  • Schwann Cells:

    • Wrap around PNS axons to form myelin sheaths.

Multiple Sclerosis (MS)

  • Autoimmune condition where immune cells attack myelin sheaths, causing plaques.

  • Results in progressive loss of body functions.

Nervous System Part 4 - Brain Development

Developmental Regions of the Brain

  • Begins as neural tube; splits into three primary vesicles:

    1. Forebrain

    2. Midbrain

    3. Hindbrain

Forebrain

  • Comprises the cerebrum with:

    • Grey matter: cell bodies and dendrites.

    • White matter: myelinated axons.

  • Includes:

    • Thalamus: sensory signal relay.

    • Hypothalamus: autonomic and endocrine system control.

    • Basal nuclei (ganglia): voluntary motor signal routing.

Key Brain Terms

  • Fissure: Separation between brain parts.

  • Gyrus: Bumps on the brain.

  • Sulcus: Valleys on the brain surface.

Nervous System Part 5 - Brain Structure and Nerves

White Matter Tracts

  • Commissural Tracts: Connect left and right hemispheres.

  • Projection Tracts: Transmit sensory/motor information between cerebrum and spinal cord.

  • Association Tracts: Longitudinal tracks within hemispheres.

Brainstem Components

  • Midbrain:

    • Below hypothalamus; involved in reflexes and eye movement.

  • Hindbrain:

    • Composed of pons (breathing regulation) and medulla oblongata (vital functions).

  • Cerebellum:

    • Coordinates motor actions.

Nervous System Part 6 - Meninges and Ventricles

Meninges

  • Three protective layers:

    1. Dura Mater: Tough outer layer.

    2. Arachnoid Mater: Web-like strands creating subarachnoid space; contains CSF.

    3. Pia Mater: Attaches directly to the brain and spinal cord.

Ventricles of the Brain

  • Lateral Ventricles: Two, connected to third ventricle.

  • Ventricles 3 and 4: Connected by cerebral aqueduct.

  • CSF is formed in all ventricles; exists in subarachnoid space.

Spinal Cord Anatomy

  • Extension of the brain stem; contains protective layers similar to the brain.

  • 31 pairs of spinal nerves with a specific structure change around L2 (conus medullaris).

  • Cauda Equina: Bundle of nerves below the conus medullaris.

Internal Structure of Spinal Cord

  • White Matter: Outer layer of myelinated axons.

  • Grey Matter: Inner layer containing cell bodies.

  • Sensory Neurons: Enter through posterior roots; motor neurons exit through anterior roots.

Spinal Nerves & Cranial Nerves

Spinal Nerves

  • Total of 31 pairs, carrying sensory and motor information.

  • Divide into posterior and anterior rami for innervation.

Plexuses

  • Cervical: Innervates neck; includes phrenic nerve (diaphragm).

  • Brachial: Innervates upper limb; notable nerves include musculocutaneous, median, ulnar, and radial nerves.

  • Lumbar/Sacral: Innervates lower limbs; includes femoral and sciatic nerves.

Cranial Nerves

  • Total of 12 pairs; include various functions and locations.

  • Mnemonics for names and functions to assist with memorization.

Autonomic Nervous System

  • Also called visceral nervous system; affects organ function.

  • Comprised of sympathetic, parasympathetic, and enteric nervous systems.

  • Operates through involuntary motor neurons; sensory information travels to the spinal cord, while motor commands exit the spinal cord.