BSC 2085 Lab 9: Nervous System Overview

Study Notes

Central Nervous System (CNS) comprises the brain and spinal cord, acting as the main integration and command center.
Peripheral Nervous System (PNS) includes cranial and spinal nerves, divided into somatic and autonomic systems, facilitating communication between the CNS and the body.

Somatic Nervous System
- Involves spinal and cranial nerves that receive sensory information and generate responses in skeletal muscles.
- Sensory nerves transmit information from peripheral receptors to the CNS.
- Motor nerves carry commands from the CNS to skeletal muscles.
Autonomic Nervous System
- Composed of autonomic sensory and motor nerves responding to cardiac muscle, smooth muscle, and glands.

Develops from a neural tube:
- Cephalic portion forms the brain.
- Caudal portion develops into the spinal cord.
Forebrain Structures
- Telencephalon: includes olfactory bulbs, cerebrum, and ventricles I and II.
- Diencephalon: includes thalamus, hypothalamus, and related glands.
Midbrain consists of the mesencephalon.
Hindbrain Structures
- Metencephalon: comprises the cerebellum and IV ventricle.
- Myelencephalon: forms the medulla oblongata.

Neurons are vital nerve cells conducting impulses; approximately 100 billion in the brain and 100 million in the spinal cord.
Key Components of Neurons
- Cell body (soma) contains the nucleus and Nissl bodies.
- Dendrites receive impulses, while the axon conducts impulses away from the cell body.
- Axon hillock connects the axon to the cell body, facilitating impulse transmission.
- Synaptic knobs form connections (synapses) with other nerve cells.

Axons are insulated by a myelin sheath, which enhances impulse conduction speed.
Myelin is produced by oligodendrocytes in the CNS and Schwann cells in the PNS.
Schwann cells wrap around nerve fibers creating the myelin sheath, and the neurilemma serves as the outer layer.
Endoneurium is the connective tissue that surrounds Schwann cells, while nodes of Ranvier are gaps between myelin segments.

Sensory (afferent) Neurons: transmit impulses from sensory receptors to the CNS.
Motor (efferent) Neurons: convey impulses from the CNS to effectors (muscles and glands).
Association (interneurons): connect different areas within the CNS.
Neurons are classified into multipolar (motor and association), unipolar (sensory), bipolar, and anaxonic categories based on their structure.

Myelinated neurons are organized into nerve tracts in the CNS and peripheral nerves.
White matter contains myelinated axons, while unmyelinated axons form gray matter.
Sensory nerves consist of sensory neurons, motor nerves consist of motor neurons, and mixed nerves contain both types.

Muscle contraction requires stimulation from motor neurons.
Motor neuron cell bodies reside in the brain/spinal cord; their axons reach targeted muscle cells.
Each axon branches to serve individual muscle cells, forming a motor unit.
The motor end plate is a synapse between the motor neuron and the muscle cell, where acetylcholine binding initiates muscle contraction.
This junction is crucial for neuromuscular communication, connecting the axon to the muscle cell.