Nervous System Overview

Neuron Structure and Function

Parts of a Neuron
- Body (Soma):
- Integrative center or control center of the neuron.
- Dendrites (Dendra):
- Receive signals from other neurons.
- Axon:
- Sends action potentials along a pathway.

Ions Involved in Action Potential:
- Sodium Ions (Na+):
- Rush into the axon to cause depolarization.
- Calcium Ions (Ca2+):
- Rush into the terminal end of the axon to trigger the release of neurotransmitters.
- Potassium Ions (K+):
- Leak out of the neuron during the repolarization phase.
Phases of Action Potential:
- Depolarization:
- Occurs when Na+ rushes in, making the neuron less negative, or more positive.
- Repolarization:
- Occurs when K+ leaks out, returning the membrane potential to below resting levels.
- Resting Membrane Potential:
- Typically at -70 mV.
- Threshold:
- The point at which an action potential will occur. It initiates an all-or-nothing response (neuron either fires or does not).

Myelin Sheath:
lipids
- Function:
- Insulates the axon and speeds up the conduction of action potentials.
- Production:
- Oligodendrocytes: In central nervous system (CNS).
- Schwann Cells: In peripheral nervous system (PNS).
- Saltatory Conduction:
- The process by which action potentials jump from node to node along a myelinated axon, enhancing speed of transmission.

Central Nervous System (CNS) Components:
- Brain
- Spinal Cord
Peripheral Nervous System (PNS):
- Comprises all other neural structures.
- Divisions of PNS:
- Motor (Efferent):
  - Sends signals from the CNS to muscles or glands.
  - somatic and autonomic
  - somatic: skeletal muscle
- Sensory (Afferent):
  - Sends signals to the CNS from sensory receptors.

Divisions of the Autonomic Nervous System (ANS):
- Sympathetic:
- Controls fight or flight responses.
- Parasympathetic:
- Controls rest and digest functions.
Tissues Innervated by ANS:
- Smooth Muscle
- Cardiac Muscle
- Glands

Meninges:
- Protective coverings of the brain and spinal cord.
- Types of Meninges:
- Dura Mater: Outer layer.
- Arachnoid Mater: Middle layer.
- Pia Mater: Inner layer.
Spinal Cord Termination:
- The spinal cord terminates at the Conus Medullaris at the level of
- L1-L2 vertebrae.

Nerve Cell Bodies:
- In PNS, called Ganglia.
- In CNS, called Nuclei.
Spinal Cord Horns:
- Dorsal Horn: Sensory functions.
- Ventral Horn: Motor functions.
- Lateral Horn: Autonomic functions.

Parts of the Brain:
- Cerebrum:
- Gray and white matter structure.
- Diencephalon:
- Composed of Thalamus, Hypothalamus, Epithalamus.
- Hypothalamus: Works with endocrine system to regulate hormones (ADH and Oxytocin).

Reflex Integration:
- Most reflexes are integrated in the spinal cord, not the brain.
Patellar Reflex:
- A stretch reflex where tapping the knee causes a contraction response due to rapid stretching of the patellar tendon.
Cranial Nerves:
- There are 12 pairs of cranial nerves in the human body. Each has a specific function and is numbered I through XII.
- Examples:
- Cranial Nerve I: Olfactory (smell).
- Cranial Nerve II: Optic (vision).
- Cranial Nerve III: Oculomotor (eye muscle movement).
- Cranial Nerve X: Vagus (visceral control).

Multiple Sclerosis (MS):
- An autoimmune disease that attacks the myelin sheath of nerves, leading to a range of neurological symptoms including tremors and impaired movement.

Importance of Understanding the Nervous System:
- Knowledge of neuron structure and function is crucial for understanding how the nervous system operates, including reflexes and responses to stimuli.
- Familiarity with cranial nerves and their functions is vital for assessments in clinical settings.
- Pathophysiology of diseases like MS highlights the clinical relevance of the anatomy and physiology of the nervous system.