BMS 600 - Fundamentals of the nervous system and nervous tissue

What is the nervous system?

Master controlling and communicating system of body

How do cells communicate?

Via electrical and chemical signals that are rapid and specific and usually cause immediate responses

What are the overlapping functions of the nervous system

Sensory input, integration and motor output

What is sensory input?

Information gathered by sensory receptors about internal and external changes

What is integration

Processing and interpretation of sensory input

What is motor output?

Activation of effector organs (muscles and glands) produces a response

What are effector organs?

Muscles and glands

What are the parts of the nervous system?

Central nervous system (CNS) and peripheral nervous system (PNS)

What is the central nervous system?

• brain and spinal cord of dorsal body cavity

• Integration and control center

  • Inteprets sensory input and dictates motor output

What is the peripheral nervous system?

• portion outside of CNS

• Consists of mainly nerves that extend from brain and spinal cord

  • Spinal nerve

  • Cranial nerves

What are spinal nerves?

To and from spinal cord

What are cranial nerves?

To and from brain

What are the functional divisions of the PNS

Sensory (afferent) division and motor (efferent) division

What is sensory (afferent) division?

• part of the PNS that transmits sensory information toward the central nervous system (brain and spinal cord) from sensory receptors in the body

• Has somatic sensory fibers and visceral sensory fibers

What are somatic sensory fibers?

Convey impulses from skin, skeletal muscles and joints to CNS

What are visceral sensory fibers?

Convey impulses from visceral organs to CNS

What is motor (efferent) division?

• Transmits impulses from CNS to effector organs

• 2 divisions

What are the sub divisions in the motor (efferent) division?

Somatic nervous system and autonomic nervous system

What is the somatic nervous system?

A voluntary nervous system that has somatic motor nerve fibers conducting impulses from CNS to skeletal muscles

What is the autonomic nervous system?

An involuntary nervous system that consists of visceral motor nerve fibers and functions to regulate smooth muscle, cardiac muscle and glands through 2 functional subdivisions

What are the subdivisions of the autonomic nervous system?

Sympathetic and parasympathetic

T/F: the sympathetic and parasympathetic division work in opposition of each other

True

What is the sympathetic division?

Mobilizes body systems during activity

What is the parasympathetic division?

Conserves energy and promotes housekeeping functions during rest

What cell types are found in nervous tissue?

Neuroglia (glial cells) and neurons (nerve cells)

What are neuroglia (glial cells)?

Small cells that surround and wrap delicate neurons

what are neurons (nerve cells)?

excitable cells that transmit electrical signals

What are the main neuroglial that support CNS neurons?

astrocytes, microglial cells, ependymal cells, oligodendrocytes

what CNS neuroglial is the most abundant?

astrocytes

what are astrocytes?

versatile and highly branched neuroglia that cling to neurons, synaptic endings and capillaries

what are the functions of the astrocytes?

• support and brace neurons

• Play role in exchanges between capillaries and neurons

• Guide migration of young neurons

• Control chemical environment around neurons

• Respond to nerve impulses and neurotransmitters

• Influence neuronal functioning

• Participate in information processing in brain

What are microglial cells?

small ovoid cells with thorny processes that touch and monitor neurons and can migrate toward injured neurons

which CNS neuroglia can transform to phagocytize microorganisms and neuronal debris and are also known as defensive cells in the CNS

Microglial cells

what are ependymal cells

line cerebrospinal fluid-filled CNS cavities and forms a permeable barrier between CSF in cavities and tissue fluid bathing CNS cells

what is the structure of ependymal cells?

Can range in shape from squamous to columnar and may be cilliated

what are oligodendrocytes?

branched cells with processes that wrap CNS nerve fibers forming insulating myelin sheaths in thicker nerve fibers

What are the neuroglia of the PNS?

satellite cells and schwann cells

what are satellite cells?

surround neuron cell bodies in PNS and function similar to astrocytes of CNS

what are schwann cells (neurolemmocytes)

surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers that are vital to regeneration of damaged peripheral nerve fibers

what PNS neuroglia has a similar function of oligodendrocytes?

schwann cells(neurolemmocytes)

What are neurons?

nerve cells that are structural units of nervous system and are large highly specialized cells that conduct impulses

what are the special characteristics of neurons?

• extreme longevity (can last a lifetime)

• Amitotic, with few exceptions

• High metabolic rate: requires continous supply of oxygen and glucose

What does amitotic mean?

Neurons lose the ability to divide and reproduce via mitosis once they reach maturity

How many cell bodies and processes do neurons have?

every neuron has a cell body and one or more processes

what is the neuron cell body

biosynthetic center and receptive region of neuron it synthesizes proteins membranes chemicals and contain rough ER

what is the structure of cell body?

contains spherical nucleus with nucleous, some contain pigments

what is the receptive region of the cell body?

in most the plasma membrane is part of receptive region that receives input info from other neurons

where are most neuron cell bodies located?

CNS

what are nuclei?

clusters of neuron cell bodies in CNS

what are ganglia?

clusters of neuron cell bodies in PNS

what are neuron processes?

Armlike process that extend from cell body

Neuron processes in CNS

bundles of neuron processes are called tracts and contains both neurons cell bodies and their processes

neuron processes in PNS

bundles of neuron processes are called nerves and the PNS contains chiefly neurons cell bodies processes (whose cell bodies are in CNS)

what are the types of neurons cell processes?

dendrites and axons

what are dendrites?

Receptive regions of a neuron that convey incoming messages toward cell body as graded potentials (short distance signals)

what neuron processes contain same organelles as in cell body?

dendrites

when are finer dendrites seen?

found in many brain areas because they are highly specialized to collect information and contain dendritic spines

what are dendritic spines?

appendages with bulbous or spiky ends

What is the structure of axon?

axon hillock, nerve fibers, axon collaterals, axon terminals/terminal boutons

what are axon hillock

each neuron as one axon that starts at cone-shaped area

how long can axons be?

in some neurons axons are short or absent; in others axons can comprise almost the entire length of the cells, some can be over 1 meter long

what are nerve fibers?

long acons

what are axon collaterals?

occasional branches in axons

what are axon terminals/terminal boutons

distal endings and axons can branch profusely at their end

What are the functional characteristics of the axon?

• conducting region of neuron

• Generates nerve impulses and transmits the along axolemma to axon terminal

  • Can carry on many conversation with different neurons at the same time

what is the axolemma?

neuron cell membrane

which part of the axon secretes neurotransmitters?

terminal region secretes neurotransmitters , which are released into extracellular space

what is the myelin sheath composed of?

myelin which is a whitish protein-lipid substance

what is the funciton of myelin?

protect and electrically insulate axons and can increase speed of nerve impulse transmission

what are myelinated fibers?

segmented sheath surrounds most long or large-diameter axons

what are nonmyelinated fibers?

do not contain sheath so the conduct impulses more slowly, surrounded by Schwann cells but no coiling

Myelination of a nerve fiber in the PNS

• schwann cell envelops an axon

• Schwann cell rotates around axon wrapping its plasma membrane loosely around it in successive layers

• Schwann cells cytoplasm is forced from between the membranes

• Tight membrane wrappings surrounding the axon form the myelin sheath

What are myelin sheaths gap?

gaps between adjacent schwann cells and sites where axon collaterals can emerge

Why are plasma membranes good electrical insulators?

they have less proteins so no channels or carriers

myelin sheaths in tthe CNS

• formed by processes of oligodendrocytes, not whole cells

• Each cell can wrap up to 60 axons at once

• Myelin sheath gap is present

What is white matter?

regions of brain and spinal cord with dense collections of myelinated fibers, usually fiber tracts

what is gray matter?

mostly neuron cell bodies and nonmyelinated fibers

How to classify neurons

neurons are grouped by the direction in which nerve impulses travels relative to CNS

what are the types of neurons?

sensory, motor, internneurons

what are sensory neurons?

• transmit impulses from sensory receptors to CNS

• Almost all are unipolar

  • Cell bodies are located in ganglia in PNS

what are motor neurons?

• carry impulses from CNS to effectors

• Multipolar

• Most cell bodies ate located in CNS (except some autonomic neurons)

What ate interneurons (association neuons)?

• between motor and sensory neurons

• Shuttle signals through CNS pathways

• Most are entirely within CNS

What type of neuron makes up 99% of body’s neurons?

internneurons

What are the types of structural morphology of neurons?

Unipolar, bipolar, psuedounipolar, multipolar

T/F: unlike most other cells, neurons can rapidly change resting membrane potential

true

what is the role of membrane ion channels?

large proteins serve as selective membrane ion channels, (K+ ion channels only allow K+ to pass through)

what are the types of ion channels?

leakage (nongated) and gated channels

what are leakage (nongated) channels

always open

what are gated channels?

part of the protein changes shaped to open/close the channel

what are the types of gated channels?

chemically gated, voltage-gated or mechanically gated

what are chemically gated (ligand-gated) channels?

open only with binding of a specific chemical (ex. Neurotransmitter)

what are voltage-gated channels?

open and close in response to changes in membrane potential

what are mechanically gated channels?

open and close in response to physical deformation of receptors, as in sensory receptors

How do ions diffuse in gated channels?

• in chemical concentration gradients from high to low concentration

• Along electrical gradients towards opposite electrical charge

What is a voltmeter?

measures potential (charge) difference across membrane of resting cell

what is the resting membrane potential of a resting neuron?

approximately -70 mV

what does it mean by the membrane is polarized?

different in electrical charges between outside and inside

which side of the membrane is more negative?

cytoplasmic side of membrane is negatively charged relative to the outside

what is the actual voltage difference?

varies from -40mV to -90mV

how are resting membrane potential generated?

differences in ionic compositiion of ICF and ECF and differences in plasma membrane permability?