Nervous Tissue and Central Nervous System: Key Structures and Functions

Nervous Tissue

Figures and Tables

Nervous tissue is specialized for communication via electrical and chemical signals. It consists of neurons and supporting cells, each with distinct structures and functions.

• Typical Neuron Structure (12.4): Neurons have dendrites (receive signals), a cell body (soma), axon hillock (initiates action potentials), axon (transmits impulses), myelin sheath (insulates axon), Schwann cells (PNS myelination), nodes of Ranvier (gaps in myelin), terminal branches, and axon terminals (release neurotransmitters).

• Neuron Structural Classification (Table 12.2): Neurons are classified as multipolar (many dendrites, one axon), bipolar (one dendrite, one axon), or unipolar (single process splits into two branches).

• Relationship Between Sensory & Motor Neurons (12.8): Sensory (afferent) neurons transmit impulses toward the CNS; motor (efferent) neurons carry impulses away from the CNS to effectors.

• Supporting Cells (12.6): Also called neuroglia, these include astrocytes, oligodendrocytes, microglia, ependymal cells (CNS), and Schwann cells, satellite cells (PNS). They support, insulate, and protect neurons.

• Nerve Structure (12.9): Nerves are bundles of axons in the PNS, surrounded by connective tissue layers: endoneurium (around each axon), perineurium (around fascicles), and epineurium (around the whole nerve).

• Reflex Arcs (12.10, 12.11): Reflex arcs are the basic functional units of the nervous system, involving a receptor, sensory neuron, integration center, motor neuron, and effector.

Slides

• Pyramidal Cells of Cerebrum: Large, triangular-shaped neurons found in the cerebral cortex, important for voluntary motor control.

• Purkinje Cells of Cerebellum: Large, flask-shaped neurons with extensive dendritic trees, crucial for motor coordination.

Central Nervous System (CNS)

Figures

• Spinal Cord (13.2, 13.24): The spinal cord is a long, thin, tubular structure that connects the brain to the peripheral nervous system. It is organized into segments and contains both gray and white matter.

• Ventricles (13.4): The brain contains four ventricles (lateral, third, and fourth) filled with cerebrospinal fluid (CSF). Key structures include the interventricular foramina, cerebral aqueduct, median & lateral apertures, and central canal.

• Brain, Sagittal Section (13.9a): A sagittal section reveals major brain regions: cerebrum, diencephalon, brainstem, and cerebellum.

• Diencephalon (13.6): Includes the thalamus, hypothalamus, and epithalamus. It acts as a relay center and regulates autonomic functions.

• Lobes of the Brain (13.11): The cerebrum is divided into frontal, parietal, temporal, and occipital lobes, each with specialized functions.

• Basal Nuclei (13.17): Deep gray matter structures involved in movement regulation. Note the relationships among basal nuclei, thalamus, and ventricles.

• Limbic System (13.19): A group of structures involved in emotion, memory, and motivation. Includes the hippocampus, amygdala, and parts of the diencephalon.

• Meninges (13.21): Three protective membranes covering the CNS: dura mater (outer), arachnoid mater (middle), and pia mater (inner).

• Circulation of CSF (13.23): CSF is produced by the choroid plexus, circulates through the ventricles, central canal, and subarachnoid space, and is reabsorbed into the venous system. Key flow: Lateral ventricles → interventricular foramina → third ventricle → cerebral aqueduct → fourth ventricle → median/lateral apertures → subarachnoid space → arachnoid villi → dural venous sinuses.

Table: Neuron Structural Classification

Type	Structure	Location	Function
Multipolar	Many dendrites, one axon	Most CNS neurons	Motor and interneurons
Bipolar	One dendrite, one axon	Retina, olfactory epithelium	Sensory (special senses)
Unipolar	Single process splits into two branches	Sensory ganglia of PNS	Sensory (general senses)

Example: Reflex Arc

• Step 1: Receptor detects stimulus (e.g., pain in skin).

• Step 2: Sensory neuron transmits impulse to CNS.

• Step 3: Integration center processes information (may involve interneurons).

• Step 4: Motor neuron carries impulse to effector.

• Step 5: Effector (muscle or gland) produces response (e.g., withdrawal from pain).

Additional info:

• CSF functions to cushion the brain, remove waste, and maintain homeostasis.

• Neuroglia outnumber neurons and are essential for nervous system health and function.