Nervous system

• Nervous system


  Consists of two divisions: the central nervous system containing the brain and spinal cord, and the peripheral nervous system which is a network of nerves and neural tissues branching out throughout the body
• Neurons


  • The nerve cells, the structural and functional units of the nervous system
  • They conduct impulses that enable the body to interact with its internal and external environments
• Types of neurons


  • Motor neurons
  • Sensory neurons
  • Interneurons
• Motor neurons


  • Usually have one axon and several dendrites
  • The axon is covered with an insulating fatty layer called a myelin sheath, and transmits signals a long distance from the neuron to the area to be activated
  • Dendrites are short and unsheathed
  • Cause muscle contractions and control secretions from glands and organs, controlling body functions
• Sensory neurons


  • Do not have true dendrites
  • Attached to sensory receptors and transmit impulses to the central nervous system, which then stimulate the interneurons, and then motor neurons
• Interneurons


  • Located entirely within the central nervous system
  • Intercept the impulses from the sensory neurons and transmit the signals to the motor neurons
• Nerve fibers


  • No Schwann cells on nerve fibers in the central nervous system, therefore damage to those nerve fibers is not reversible
  • A bundle of nerve fibers is simply called 'a nerve'
  • AFFERENT nerves conduct impulses to the central nervous system
  • EFFERENT nerves conduct impulses to the muscles, organs, and glands
• Schwann cells


  • Only found on peripheral nerves which can regenerate
• Myelin sheath


  • A fatty layer of insulation on some nerve fibers
• Axon


  • Transmits the message
• Synapses


  • Connectors hooking dendrites and axons from one neuron to another
  • The number of synapses influences transmission, and can decrease with disease, lack of stimulation, drug use, etc.
• Gray matter


  • Unsheathed nerve fibers (cannot be regenerated if damaged) in the cortex or surface layer of the brain and spinal cord
• White matter


  • Myelinated nerve fibers in the internal structure of the brain and spinal cord
• Meninges


  • The 3 membranes (dura mater, arachnoid, pia mater) that enclose the brain and spinal cord
• Cerebrum


  • Governs all sensory and motor activity, including sensory perception, emotions, consciousness, memory, and voluntary movements
  • Divided into left and right hemispheres
  • Surface or cortex is arranged in bulging folds (gyri) and furrows (sulci)
  • Divided into 4 lobes: frontal (motor activity, personality, speech), parietal (language, temperature, pressure, touch), temporal (hearing, smell, language input), occipital (vision)
• Cerebellum


  • Contains nerve fibers that connect it to every part of the central nervous system
  • Coordinates voluntary and involuntary patterns of movements
  • Adjusts muscles to automatically maintain posture
• Diencephalon


  • Consists of the thalamus (relay center for all sensory impulses except olfactory and motor areas of the cortex) and the hypothalamus (regulates behavior, emotional expression, body temperature, metabolic activities, and hormonal secretions)
• Brainstem


  • Consists of the midbrain (controls visual reflexes and sense of hearing), pons (plays a role in regulating visceral control), and medulla oblongata (connects the brain to the spinal cord and regulates breathing, swallowing, coughing, sneezing, vomiting, heartbeat, and blood pressure)
• Spinal cord


  • 31 segments corresponding to vertebrae, with left and right pairs of sensory and motor nerves branching out to the peripheral nervous system
  • Shorter than the spinal column, so segments do not perfectly correspond to the vertebrae
• Cerebrospinal fluid


  A colorless fluid produced in the ventricles of the brain, surrounding the brain and spinal cord to cushion them from shocks
• Cranial nerves


  • Olfactory (smell)
  • Optic (vision)
  • Oculomotor (eye and eyelid muscles)
  • Trochlear (eyeball)
  • Trigeminal (face, nose, mouth, forehead, top of head, jaw)
  • Abducens (eyeball)
  • Facial (face and scalp muscles, part of tongue for taste)
  • Auditory/cochlear (hearing and equilibrium)
  • Glossopharyngeal (saliva, swallowing, taste)
  • Vagus (heart, lungs, stomach, intestines)
  • Accessory (head and shoulder movement)
  • Hypoglossal (tongue muscles)
• Autonomic nervous system


  • Part of the peripheral nervous system, controls involuntary bodily functions like sweating, gland secretions, blood pressure, and heart rate
  • Divided into sympathetic (flight or fight responses) and parasympathetic (restoring homeostasis) divisions