PSYC271 Chapter 3: Anatomy of the Nervous System
3.1 General Layout of the Nervous System
Divisions of the Nervous System:
Central Nervous System (CNS): brain & spine.
Peripheral Nervous System (PNS): located outside the skull & spine.
Somatic Nervous System: interact with external environment.
Afferent Nerves: carry sensory signals from skin, muscles,
eyes, ears, etc. to CNS
Efferent Nerves: carry motor signals from the CNS to the
Autonomic Nervous System: regulates body’s internal
Afferent nerves carry sensory signals from internal organs to
CNS. Efferent carry motor signals from CNS to internal organs.
2 kinds of efferent nerves:
Sympathetic Nerves: project from the CNS in the lumbar
(lower back) & thoracic (chest) areas of the spinal cord
Parasympathetic Nerves: project from the brain or from
the sacral region of the spinal cord.
Neither carry the signal all the way to organ. Both send
signal through neurons/synapses until they reach organ.
Sympathetic nerves stimulate, organize, and mobilize energy resources in
threatening situations, whereas parasympathetic nerves act to conserve
Each autonomic target organ receives opposing sympathetic and
parasympathetic input, and its activity is thus controlled by relative levels
of sympathetic and parasympathetic activity
Sympathetic changes are indicative of psychological arousal.
Parasympathetic changes are indicative of psychological relaxation.
Most nerves from the peripheral nervous system leave from the spinal
cord, except for 12 pairs of cranial nerves which leave from the brain
(most are both sensory and motor)
Meninges, Ventricles, and Cerebrospinal Fluid:
Meninges: the 3 protective membranes that cover the brain and spinal cord
Outer layer: Dura mater
Middle layer: Arachnoid membrane, followed by subarachnoid membrane
Inside later: Pia mater ▯ attaches to surface of CNS
Cerebrospinal Fluid: also protects CNS, fills subarachnoid space & cerebral
ventricles, central canal of spinal cord (all of these interconnected). Supports and
cushions the brain.
Central Canal: thin canal that runs that length of the spinal cord
Cerebral Ventricles: four large internal chambers of the brain
Choroid Plexus: produces cerebrospinal fluid. A network of capillaries that
protrude into the ventricles from the pia mater. Hydrocephalus: when a tumor blocks a channel of one of the ventricles,
causing buildup of cerebrospinal fluid and expansion of the ventricles, and
eventually the entire brain. Fluid must be drained.
BloodBrain Barrier: the mechanism that keeps certain toxic substances in the
blood from passing into brain tissue. Barrier created by special structure of tightly
packed cerebral blood vessels
The degree to which therapeutic and recreational drugs can influence brain
activity depends on the ease with which they penetrate the bloodbrain barrier
3.2 Cells of the Nervous System
2 different types of nervous system cells: neurons & glial cells
Anatomy of Neurons:
Neuron: cell specialized for the reception, conduction, and transmission of
External Anatomy of Neurons: neuron diagrams p. 55/56
Cell Body: metabolic center of neuron ‘soma’
Myelin: fatty insulation around many axons
Axon, cell membrane, axon hillock, synapse
Nodes of Ranvier: gaps between sections of myelin
Buttons: ending of the axon. Release chemicals into synapse.
Internal Anatomy of Neurons:
Endoplasmic Reticulum: rough portions (with ribosomes) synthesize
proteins, smooth proteins synthesize fats
Ribosomes: synthesize proteins
Mitochondria: aerobic (oxygenconsuming) energy release
Nucleus: holds DNA
Microtubules: rapid transport of material through neurons
Synaptic Vesicles: store neurotransmitters
Neurotransmitters: influence activity of other cells
Neuron Cell Membrane:
Neuron cell membrane composed of lipid bilayer embedded with
proteins. Some proteins are ‘channel proteins’, ▯allow molecules to pass
through the layer. Others are ‘signal proteins’ ▯send message to inside of
neuron when molecule binds to protein.
Classes of Neurons:
Multipolar Neuron: neuron with more than 2 processes extending from
its cell body
Unipolar Neuron: one process extending from cell body
Bipolar Neuron: 2 processes
Interneurons: neurons with short or no axon. Integrate neural activity
within a single brain structure (don’t conduct signals from one neuron to
another). Gather all info.
Neurons and Neuroanatomical Structure: Nuclei: in CNS, composed primarily of cell bodies
Ganglia: in Peripheral NS, composed primarily of axons.
Tracts: bundles of axons found in the CNS
Nerves: bundles of axons found in the PNS.
Glial Cells: nonneural cells of the nervous system. Not totally understood.
Oligodendrocytes (1): glial cells that myelinate axons of the CNS
Myelin Sheath: increase speed and efficiency of axonal conduction
Schwann Cells (2): glial cells that compose the myelin sheaths of PNS axons
and promote their regulation
Difference between Schwann and Oligodendrocytes: each Schwann cell
constitutes one myelin segment. One Oligodendrocyte can provide several myelin
segments. Also only Schwann cells can guide axonal regrowth.
Microglia (3): respond to injury/disease by multiplying, engulfing cellular
debris, and triggering inflammatory responses
Astrocytes (4): largest glial cells. Allow passage of some chemicals from blood
to CNS neurons, and block others. Also provide nutrients and support for other
neurons and maintain synapses.
3.3 Neuroanatomical Techniques and Directions
Golgi Stain: a neural stain that completely darkens a few of the neurons in each
slice of tissue, thereby revealing their silhouettes
Nissl Stain: a neural stain that has an affinity for structures in neuron cell bodies
Electron Microscopy: used to study the fine details of cellular structure.
Neuroanatomical Tracing Techniques: can be either anterograde (forward) or
retrograde (backward) tracing methods.
Directions in the Vertebrate Nervous System:
Vertebrate nervous system has 3 axes: anteriorposterior, dorsalventral, medial
Anterior: towards noseend of vertebrae
Posterior: toward tailend of vertebrae or toward back of the head
Dorsal: toward surface of the back of vertebrae or top of head