Chapter 10

Nervous System Overview

• The nervous system is divided into two main divisions:

  • Central Nervous System (CNS): Includes the brain and spinal cord, enclosed in the dorsal cavity.

  • Peripheral Nervous System (PNS): Includes nerves that connect the CNS with the rest of the body.

Functions of the Nervous System

• Sensory Function: Gathers information from the environment (internal and external) and carries it to the CNS (e.g., visual information from the eye).

• Integrative Function: Interpretation of sensory information; involves memory and decision-making based on prior knowledge (e.g., recognizing a cat's behavior).

• Motor Function: Sends information from the CNS to muscles and glands, executing plans made by the CNS (e.g., feeding the cat).

Cellular Composition of the Nervous System

Neuroglia vs. Neurons

• Neuroglia (Glial Cells):

  • Support and protect neurons; do not conduct nerve impulses.

  • Major types include astrocytes (support, protect the blood-brain barrier) and ependymal cells (produce cerebrospinal fluid).

• Neurons:

  • Conduct electrical signals (action potentials).

  • Comprised of dendrites (receive signals), cell body (process signals), and axon (transmit signals).

  • Neurons can be sensory, motor, or interneurons.

Myelin Sheath Function

• Myelin sheath insulates the axon, allowing faster signal transmission.

• Formed in the PNS by Schwann cells; in the CNS by oligodendrocytes.

Transmission of Information in Neurons

• Nerve impulses travel along dendrites to the cell body and then down the axon to reach axon terminals, where neurotransmitters are released.

• The nerve impulse, known as action potential, involves:

  1. Depolarization: Sodium (Na+) ions flow into the neuron, making the inside of the cell positive.

  2. Repolarization: Potassium (K+) ions flow out, restoring the negative charge inside the neuron.

Structure and Function of the Brain

• The brain is divided into four major areas:

  1. Cerebrum: Largest part; responsible for higher functions (thinking, memory). Contains four lobes:

     • Frontal Lobe: Executive functions, voluntary motor activity, personality.

     • Parietal Lobe: Sensory information, taste, speech.

     • Temporal Lobe: Auditory functions, olfaction.

     • Occipital Lobe: Vision processing.

  2. Diencephalon:

     • Thalamus: Relay station for sensory information.

     • Hypothalamus: Regulates autonomic and endocrine system functions, maintains homeostasis.

  3. Brain Stem:

     • Midbrain: Reflexes for vision and hearing.

     • Pons: Connects higher brain and cerebellum; regulates respiration.

     • Medulla Oblongata: Vital functions (heart rate, blood pressure).

  4. Cerebellum: Coordination of voluntary movements, balance, fine motor skills.

Protective Structures for CNS

• Bone: Skull encases the brain; vertebral column surrounds the spinal cord.

• Meninges: Three layers of protective tissue (dura mater, arachnoid mater, pia mater).

• Cerebrospinal Fluid (CSF): Cushions the CNS, delivers nutrients and removes waste; formed in the choroid plexus.

• Blood-Brain Barrier: Selective barrier that prevents harmful substances from entering the CNS.

Synaptic Transmission

• Synapse: Gap between two neurons where information is transmitted chemically.

  1. Nerve impulse reaches the axon terminal, causing neurotransmitter vesicles to release their contents into the synaptic cleft.

  2. Neurotransmitters bind to receptors on the postsynaptic neuron, triggering a new nerve impulse.

Neuroplasticity

• The brain's ability to adapt and change in response to experience, injury, or disease.

• Involves reorganization of neural pathways based on learning and memory contribute to resilience after injuries.