Nervous System Anatomy

Nervous System

• The nervous system consists of two divisions: central nervous system (brain and spinal cord) and peripheral nervous system (network of nerves and neural tissues).
• Neurons are the nerve cells, the structural and functional units of the nervous system, conducting impulses that enable the body to interact with its internal and external environments.

Types of Neurons

• Motor neurons: have one axon and several dendrites, transmit signals to muscles and glands, and control body functions.
• Sensory neurons: do not have true dendrites, attached to sensory receptors, and transmit impulses to the central nervous system.
• Interneurons: located entirely within the central nervous system, intercept impulses from sensory neurons and transmit signals to motor neurons.

Nerve Fibers

• Schwann cells: only found on peripheral nerves, can regenerate.
• Myelin sheath: a fatty layer of insulation on some nerve fibers.
• Axon: transmits the message.
• Nerve fibers in the central nervous system do not have Schwann cells, making damage to those fibers irreversible.
• A bundle of nerve fibers is called a nerve.

Synapses

• Nerve impulses are transmitted via synapses, connecting dendrites and axons from one neuron to another.

Brain and Spinal Cord

• The brain and spinal cord are enclosed by three membranes: dura mater, arachnoid, and pia mater.

Parts of the Brain

• Cerebrum: governs all sensory and motor activity, including sensory perception, emotions, consciousness, memory, and voluntary movements.
• Cerebellum: coordinates voluntary and involuntary patterns of movements.
• Diencephalon: includes thalamus and hypothalamus.
• Thalamus: relay center for sensory impulses except olfactory (sense of smell) and motor areas of the cortex.
• Hypothalamus: regulates behavior, emotional expression, body temperature, and many metabolic activities.
• Brainstem: includes midbrain, pons, and medulla oblongata.
• Midbrain: controls visual reflexes and sense of hearing.
• Pons: plays a role in regulating visceral (internal organ) control.
• Medulla oblongata: connects the rest of the brain to the spinal cord, regulates breathing, swallowing, coughing, sneezing, vomiting, heartbeat, and blood pressure.

Spinal Cord

• The spinal cord has 31 segments, corresponding to the vertebrae.
• The spinal cord is shorter than the spinal column.

Cerebrospinal Fluid

• A colorless fluid produced in the ventricles of the brain, surrounding the brain and spinal cord, and cushioning them from shocks that could cause injury.

Peripheral Nervous System

• The network of nerves branching out throughout the body from the brain and spinal cord.
• Autonomic nervous system: a part of the peripheral nervous system, controlling involuntary bodily functions such as sweating, gland secretions, blood pressure, and the heart.
• Autonomic nervous system is divided into sympathetic and parasympathetic divisions.
• Sympathetic nervous system: responsible for the 'flight or fight' responses, increasing alertness, metabolic rate, respiration, blood pressure, heart rate, and sweating, and decreasing digestive and urinary function.
• Parasympathetic nervous system: counteracts the responses of the sympathetic system, restoring homeostasis.