Nervous System Overview

Functions of the Nervous System

The nervous system is responsible for coordinating and regulating bodily activities through rapid communication. It is essential for sensation, integration, and response.

• Sensory Input: Detects changes in the internal and external environment.

• Integration: Processes and interprets sensory information to determine appropriate responses.

• Motor Output: Initiates actions by activating effector organs (muscles and glands).

Central and Peripheral Nervous Systems

Central Nervous System (CNS)

The CNS consists of the brain and spinal cord. It serves as the main control center for processing information and directing responses.

• Brain: Responsible for higher functions such as thought, memory, and emotion.

• Spinal Cord: Conducts signals between the brain and the rest of the body; involved in reflex actions.

Peripheral Nervous System (PNS)

The PNS includes all neural structures outside the CNS. It connects the CNS to limbs and organs.

• Somatic Nervous System: Controls voluntary movements by innervating skeletal muscles.

• Autonomic Nervous System: Regulates involuntary functions such as heart rate and digestion.

Functional Divisions of the Nervous System

Sensory (Afferent) vs. Motor (Efferent) Divisions

The nervous system is functionally divided into sensory and motor pathways.

• Sensory (Afferent) Division: Transmits impulses from sensory receptors to the CNS.

• Motor (Efferent) Division: Carries impulses from the CNS to effector organs.

Example: Touching a hot surface activates sensory neurons (afferent), which send signals to the CNS. The CNS then sends motor signals (efferent) to withdraw the hand.

Somatic vs. Autonomic Divisions

The motor division is further subdivided:

• Somatic Nervous System: Controls voluntary movements (skeletal muscles).

• Autonomic Nervous System: Regulates involuntary activities (smooth muscle, cardiac muscle, glands).

Comparison: The somatic system is under conscious control, while the autonomic system operates automatically.

Two Main Functional Divisions

• Afferent (Sensory) Division

• Efferent (Motor) Division

Cell Types in Nervous Tissue

Neurons and Glial Cells

Nervous tissue contains two main cell types:

• Neurons: Specialized for transmitting electrical signals.

• Glial Cells (Neuroglia): Support, protect, and nourish neurons.

Action Potential Phases

Phases of an Action Potential (Nerve Signal)

An action potential is a rapid change in membrane potential that allows neurons to transmit signals.

1. Resting Membrane Potential: The neuron is at rest, with a typical potential of about -70 mV.

2. Depolarization: Sodium (Na+) channels open, causing Na+ influx and the membrane potential to become more positive.

3. Repolarization: Potassium (K+) channels open, K+ exits the cell, restoring the negative membrane potential.

4. Sodium-Potassium ATPase Pump: Restores ion gradients by pumping Na+ out and K+ in, using ATP.

Equation:

Signal Transmission at Synapses

Steps of Signal Transmission

Signal transmission at a synapse involves several steps, similar to those at the neuromuscular junction.

1. Action potential arrives at the presynaptic terminal.

2. Voltage-gated Ca2+ channels open; Ca2+ enters the cell.

3. Synaptic vesicles release neurotransmitter into the synaptic cleft.

4. Neurotransmitter binds to receptors on the postsynaptic membrane.

5. Postsynaptic membrane potential changes (depolarization or hyperpolarization).

6. Neurotransmitter is removed from the synaptic cleft (reuptake, degradation, or diffusion).

Glial Cells and Their Functions

Types and Functions of Glial Cells

Glial cells support and protect neurons. Each type has specialized functions.

Additional info: The above notes expand on the original questions by providing definitions, examples, and context for each concept, making the guide suitable for exam preparation in Anatomy & Physiology.