BY 115 Nervous Tissue & Brain

Functions of the Nervous System

Sensory input, integration, motor output

Sensory input

Detects changes inside and outside the body

Integration

Processes and interprets information

Motor output

Produces responses through muscles and glands

Structural organization of the nervous system

Central nervous system (CNS: brain and spinal cord); peripheral nervous system (PNS: cranial nerves, spinal nerves, ganglia)

Sensory nervous system

Afferent (towards CNS); carries information from receptors to CNS; consists of somatic sensory system and visceral sensory system

Somatic sensory system

Touch, pain, pressure, vibration, proprioception (determining where the body is located/positioned in 3D)

Visceral sensory system

Internal organs, vessels

Motor nervous system

Efferent (away from CNS); carries information from CNS to effectors (muscles or glands); consists of somatic motor system and autonomic motor system

Somatic motor system

Skeletal muscle

Autonomic/visceral motor system

Cardiac muscle, smooth muscle, glands

Sympathetic nervous system

Flight, fight, or stress response

Parasympathetic nervous system

Rest and digest

Collection of neuronal cell bodies

Nucleus in CNS and ganglion in PNS

Bundle of axons

Tract in CNS and nerve in PNS

Gray matter

Primarily neuronal cell bodies, dendrites, synapses, and unmyelinated processes; forms cerebral cortex and nuclei (clusters of neuron cell bodies)

White matter

Composed primarily axons, many are myelinated, and tracts (axons within CNS organized into bundles)

ID 1

Gray matter

ID 2

White matter

Neurons

Electrically excitable; receive and transmit information

Glial cells

Support cells of nervous tissue, protect and nourish neurons, and maintain neural environment; generally do not generate action potentials; can undergo mitosis; 4 types in CNS and 2 types in PNS

Astrocytes

CNS glial cells; support blood-brain barrier; regulate extracellular environment; participate in scar formation

ID 1

Astrocyte

Action potential

Electrical change in a neuron that’s used for signaling

Cell body (soma)

Contains nucleus and nucleolus; major metabolic and integrative region of neuron—integrates incoming information; contains chromatophilic substance (Nissl bodies)

Nissl bodies

Clusters of endoplasmic reticulum and ribosomes; produces proteins

Axon hillock

Region where the axon begins

ID 1

Cell body

ID 2

Axon hillock

ID 1

Cell body

ID 2

Nissl bodies

ID 3

Axon hillock

Dendrites

Receive information and carry information toward the cell body

Axon

Carries information away from the cell body

Pathway of input and output in a neuron

Dendrites to cell body to axon to axon terminals

ID 3

Axon

ID 4

Dendrites

Basic structure of a synapse

Presynaptic terminal, synaptic cleft, postsynaptic cell

Presynaptic terminal

Synaptic knob that contains vesicles with neurotransmitter

Synaptic cleft

Space between cells

Postsynaptic cell

Receives the chemical signal

Cell communication

Electrical signal arrives, neurotransmitter crosses the cleft, next cell receives the signal

ID 1

Synaptic cleft

ID 2

Presynaptic terminal

ID 3

Postsynaptic cell

Multipolar neurons

One axon, many dendrites; most common; most motor neurons and interneurons

Bipolar neurons

One axon, one dendrite; associated with special senses (retina and olfactory pathways)

Unipolar/pseudounipolar neurons

Single process that divides; most sensory neurons; cell bodies commonly located in sensory ganglia (dorsal root ganglion)

ID

Unipolar neuron

ID

Bipolar neuron

ID

Multipolar neuron

Interneurons

Located primarily in CNS; process and integrate information; connect neurons within CNS

Basic reflex arc

Receptor → sensory/afferent neuron → CNS (with possible participation from interneuron) → motor/efferent neuron → effector

ID 1

Skin receptors

ID 2

Sensory neuron

ID 3

Cell body of sensory neuron

ID 4

Posterior/dorsal root ganglion

ID 5

Interneuron

ID 6

Motor neuron

ID 7

Efferent transmission

ID 8

Axon

ID 9

Skeletal muscle

ID 10

Spinal cord

ID 11

Dendrites

ID 12

Afferent transmission

Converging neural circuit

Many neurons become one neuron

Diverging neural circuit

One neuron becomes many neurons

ID

Converging neural circuit

ID

Diverging neural circuit

Ependymal cells

CNS glial cells; line ventricles and central canal; help form choroid plexus/produce cerebrospinal fluid (CSF)

Astrocytes and ependymal cells

Maintain the CNS environment

ID 1

Ependymal cells

Microglia

CNS glial cells; immune-defense cells that remove debris by phagocytosis

Oligodendrocytes

CNS glial cells; form myelin around axons; one cell can myelinate portions of multiple axons

ID 1

Oligodendrocytes/CNS myelination

Satellite cells

PNS glial cells; surround neuron cell bodies in ganglia; help regulate the local environment

Neurolemmocytes/Schwann cells

PNS glial cells; form myelin around axons; one cell myelinates one segment of one axon; support PNS axon regeneration

ID 1

Neurolemmocytes

Myelin

Layers of glial cell membrane around an axon; electrically insulates the axon and increases conduction speed (saltatory conduction)

Myelinated axons

Myelin interrupted by nodes of Ranvier/neurofibril nodes; conduct signals faster than unmyelinated axons

Saltatory conduction

Signal travels rapidly from node to node

CNS Axon regeneration

Extremely limited; oligodendrocytes and scar tissue from astrocytes inhibit regrowth

PNS Axon regeneration

More successful than in CNS; some damaged axons can regenerate; cell body must remain intact; neurolemmocytes help guide regrowth

Nerve

Bundle of parallel axons in the PNS; peripheral nerves contain neurolemmocytes, connective tissue, blood vessels; may contain sensory axons, motor axons, or both (mixed nerve)

Connective-tissue wrappings of a nerve

Endoneurium, epineurium, perineurium

Endoneurium

Surrounds axon; made of dense regular CT

Perineurium

Surrounds fascicle; made of dense irregular CT

Epineurium

Surrounds whole nerve; made of areolar CT

Brain regions

Cerebrum, diencephalon, midbrain, pons, medulla oblongata, cerebellum

Brainstem

Midbrain, pons, medulla oblongata; connects cerebrum, diencephalon, and cerebellum to spinal cord; contains ascending (sensory) tracts and descending (motor) tracts

Surficial brain anatomy

Outer surface is folded; ridges = gyri, depressions between ridges = sulci; deep sulci = fissures

Structures that protect the brain

Cranial bones (physical protection), cerebrospinal fluid (cushions and supports the brain), Blood-brain barrier (regulates movement of substances from blood into nervous tissue), meninges (connective tissue coverings)

Cranial meninges

Three connective tissue layers that enclose and protect blood vessels supplying brain; help contain and circulate cerebrospinal fluid

Pia mater

Innermost, adheres to brain surface; thin layer of areolar connective tissue

Arachnoid mater

Lies external to pia mater

Subarachnoid space

Contains cerebrospinal fluid

Subdural space

Lies between dura mater and arachnoid mater; can develop when bleeding separates the membranes; normally a potential space

Dura mater

Tough, outer membrane, made of dense irregular connective tissue in two layers: meningeal layer (deep) and periosteal layer (superficial)

Dural venous sinuses

Dural layers separate to form; drain venous blood from the brain via the jugular vein

Epidural space

Potential space between skull and dura; can form when bleeding separates dura from skull