Nervous System Overview

• The nervous system detects and responds to changes.
• Together with the endocrine system, the nervous system controls body functions and maintains homeostasis.
• Nervous system stimulation provides immediate responses.
• Endocrine activity is slower and more prolonged in comparison.

Divisions of the Nervous System

• Central nervous system includes the brain and spinal cord.
• Peripheral nervous system consists of all other nerves.

Peripheral Nervous System Divisions

• Sensory division
• Motor division:
  • Voluntary somatic nervous system
  • Involuntary autonomic nervous system - Sympathetic ("fight or flight") - Parasympathetic ("rest and digest")

Types of Nervous Disorders

• Central nervous system disorders include, Brain tumors, Encephalitis, Epilepsy, Meningitis, Multiple Sclerosis, Alzheimer's, Parkinson's and Huntington's
• Peripheral nervous system disorders include Peripheral neuropathy, Diabetic polyneuropathy, Guillain-Barre syndrome, Sciatica and Facial nerve paralysis.

Causes of Nervous Disorders

• Congenital issues
• Vascular problems
• Infections (fungal, viral, bacterial, parasitic)
• Degenerative conditions
• Trauma
• Environmental factors.
• Risk Factors include habits, other conditions, gender, age, and genetics.

Nervous Tissue Cells

• Neurons
• Schwann cells
• Neuroglial/glial cells

Neuron Features

• Cell body forms the gray matter, found at the brain's periphery and spinal cord's center, contains a well-developed nucleus and organelles like mitochondria.
• Axon functions as the communication route, conducting electrical impulses away from the neuron's cell body, large axons in the peripheral nervous system are surrounded by a myelin sheath (Schwann cells).
• Schwann cells form the myelin sheath along the axon, with Nodes of Ranvier in between, providing insulation.
• Dendrites are extensions of the cell body that provide a large surface area for receiving information.
• Nodes of Ranvier, exposed areas between Schwann cells, assist in rapid action potential transmission in myelinated neurons.
• Synaptic end bulb allows for nerve impulse conduction, and is enclosed in a synaptic vesicle.

Neuron Properties

• Irritability is the ability to initiate nerve impulses in response to stimuli.
• Conductivity is the ability to transmit nerve impulses.

Neurological Cells

• Microglia are mainly found in blood vessel areas, they enlarge and become phagocytic during inflammation and cell destruction.
• Astrocytes form the central nervous system's main supporting tissues, are star-shaped and lie in a mucopolysaccharide ground substance near blood vessels.
• Oligodendrocytes, smaller than astrocytes, cluster around neuron cell walls in the CNS, forming and maintaining myelin.

Blood-Brain Barrier

• A selective barrier protects the brain from toxic substances and chemical variations.
• Oxygen, CO2, glucose, and lipid-soluble substances can quickly cross into the brain.
• Large molecules, drugs, inorganic ions, and amino acids pass slowly or not at all into the brain.

Nerve Impulses

• Initiated by stimulation of sensory nerve endings or passage of an impulse.

• Nerve impulses travel in one direction.

• Nerves can only send one message at one speed but the frequency/number of pulses vary

• Afferent impulses run to the brain and CNS (sensory).

• Efferent impulses run from the brain and CNS (motor).

Nerve Impulse

• Transmission of action potential is carried out by movement of ions.
• In the resting state, the nerve cell membrane is polarized due to differences in ion concentrations.
• A different electrical charge is on each side of the membrane, called the resting membrane potential.
• At rest, the charge on the outside is positive and inside it is negative.
• Main ions include sodium (Na+) and potassium (K+).

Brain Components

• Cerebrum is the largest part of the brain, facilitates mental activity, memory, sensory perception, initiation, and control of voluntary muscle contraction.
• Thalamus, sensory receptors in the skin & viscera send info about touch, pain & temperature, Input from the special sense organs travels here too where there is perception but only in basic form
• Hypothalamus controls the output of hormones and effectors of the autonomic nervous system.
• Midbrain has nuclei and nerve fibers connecting the cerebrum with the lower brain and spinal cord; important for auditory and visual reflexes.
• Pons processes information from several cranial nerves.
• Medulla oblongata is continuous with the spinal cord, controls cardiovascular, and respiratory centers, as well as reflexes.
• Cerebellum plays a role in motor movement and balance control.

Cerebrospinal Fluid (CSF)

• CSF is a clear, colorless fluid occupying the subarachnoid space.

CSF Functions

• Protection
• Buoyancy
• Excretion of waste products
• Endocrine medium for the brain

Peripheral Nervous System Composition

• Cranial nerves
• Spinal nerves
• Peripheral nerves

Peripheral Nervous System Contents

• Sensory neurons
• Motor neurons

Autonomic Nervous System

• The sympathetic nervous system activates the "fight or flight" response.
  • Needed for short-term survival.
• The parasympathetic nervous system restores the body to a state of calm ("rest and digest").
  • Needed for long-term survival.