1103 9 Nervous System

Nervous System Overview

  • The nervous system is divided into two main parts: Central Nervous System (CNS) and Peripheral Nervous System (PNS).

Organization and Functions

I. Objectives of Nervous System

  • Describe organization and functions of principal components.

  • Structure and function of neuron, glia, ganglion, nerve, gray matter, tract, white matter, sensory and motor neurons.

  • Main brain areas and their functions.

  • Structure and functions of the spinal cord.

  • Components and operation of reflex arcs.

  • Function of the autonomic nervous system (ANS), including sympathetic and parasympathetic divisions.

Central and Peripheral Nervous Systems

Central Nervous System (CNS)

  • Components include brain and spinal cord.

Peripheral Nervous System (PNS)

  • Composed of cranial nerves and spinal nerves.

  • Includes ganglia and autonomic nervous system components.

Anatomy of the Brain

Major Areas of the Brain

  • Cerebrum: responsible for sensory processing and motor function.

  • Diencephalon: includes thalamus (sensory relay) and hypothalamus (homeostasis).

  • Brain Stem: consists of midbrain, pons, and medulla; controls basic life functions.

  • Cerebellum: coordinates balance and motor control.

Nervous System Terminology

  • Tracts: bundles of axons within the CNS.

  • Nerves: bundles of axons within the PNS.

  • Ganglia: collections of nerve cell bodies outside the CNS.

  • Gray Matter: neuron cell bodies and dendrites in CNS.

  • White Matter: myelinated axons in CNS.

Neurons and Support Cells

  • Neurons: transmit nerve impulses; consist of dendrites, cell body, axon.

  • Glia (neuroglia): support cells that protect and nourish neurons.

Reflex Arcs

  • Components include sensory neuron, integrating center, motor neuron, and effector (muscle/gland).

  • Reflex arcs enable rapid responses to stimuli (e.g., knee-jerk reflex).

Spinal Cord Functions

  • Communication between brain and periphery.

  • Carries sensory impulses to the brain and motor impulses to the body; facilitates spinal reflexes.

Resting Membrane Potential

  • Neurons maintain a polarized state, typically around -70 mV, due to ion concentration gradients.

  • High K+ concentration inside the cell, high Na+ outside; established by active transport pumps (Na+/K+).

Action Potentials

  • Generated when depolarization reaches a threshold.

  • The signal travels along the axon, facilitated by myelin sheaths and saltatory conduction.

Neurotransmission

  • Synapses allow communication between neurons; neurotransmitters are released at chemical synapses.

  • Examples include acetylcholine (muscle action), glutamate (excitatory), GABA (inhibitory).

Autonomic Nervous System

  • Divided into sympathetic (fight-or-flight response) and parasympathetic (rest-and-digest).

  • Regulates involuntary functions like heart rate and digestion.

  • Uses different neurotransmitter systems to mediate responses.