Unit 4 - Anatomy and Physiology

• Afferent nervous pathway:

• Sensory input

• Direction: Towards the CNS (brain/spinal cord).

• Function: Detects external/internal stimuli (touch, temperature, organ status) via sensory receptors.

• "A" in Afferent = Arrive at the brain.

• Integrative nervous pathway:

• Processing

• Location: Occurs entirely within the CNS (brain and spinal cord).

• Function: Interneurons process input from afferent pathways, evaluate data, and formulate a response.

• Components: Interneurons/association neurons.

• Efferent nervous pathway: 

• Motor output

• Direction: Away from the CNS towards muscles or glands.

• Function: Executes commands (voluntary movement via somatic, involuntary via autonomic nervous system).

• "E" in Efferent = Exit the brain.

The nervous system

• Master controlling and communicating system of body

• Cells communicate via electrical and chemical signals

  • Rapid and specific

  • Usually cause almost immediate responses

Functions of the nervous system

Sensory input, integration, motor output

Sensory input

• Information gathered by sensory receipts about internal and external

Integration

• Processing and interpretation of sensory input

• Motor output

• Activation of effector organs (muscles and glands) produce response

• Central nervous system (CNS)

• Brain and spinal cord of dorsal body cavity

• Integration and control center

  • Interprets sensory input and dictates motor output

Divisions of nervous system

CNS and PNS

• Peripheral nervous system (PNS)

• The portion of the nervous system outside CNS

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

  • Spinal nerves to and from spinal cord

  • cranial nerves to and from brain

• Two functional divisions

  • Sensory (afferent) division

    • Somatic sensory fibers - convey impulses from skin, skeletal muscles, and joints to CNS

    • Visceral sensory fibers - convey impulses from visceral organs to CNS

  • Motor (efferent) division

    • Transmits impulses from CNS to effector organs

      • Muscles and glands

    • 2 divisions

      • Somatic nervous system

      • Autonomic nervous system

• Sensory (afferent) division

• Somatic sensory fibers - convey impulses from skin, skeletal muscles, and joints to CNS

• Visceral sensory fibers - convey impulses from visceral organs to CNS

• Motor (efferent) division

• Transmits impulses from CNS to effector organs

  • Muscles and glands

• 2 divisions

  • Somatic nervous system

  • Autonomic nervous system

Motor division of PNS: somatic nervous system

• Somatic motor nerve fibers

• Conducts impulses from CNS to skeletal muscles

• Voluntary nervous system

  • Conscious control of skeletal muscles

Motor division of PNS: autonomic nervous system

• Visceral motor nerve fibers

• Regulates smooth muscle, cardiac muscle, and glands

• Involuntary nervous systems

• Two functional subdivisions

  • Sympathetic (fight or flight)

  • Parasympathetic (rest or digest)

  • Work in opposition to each other

Histology of nervous tissue

• Highly cellular; little extracellular space

  • Tightly packed

• 2 principal cell types

  • Neuroglia - small cells that surround and wrap delicate neurons

  • Neurons (nerve cells) - excitable cells that transmit electrical signals

• Neuroglia

• small cells that surround and wrap delicate neurons

• Neurons (nerve cells)

• excitable cells that transmit electrical signals

Histology of nervous tissue: neuroglia

• Astrocytes (CNS)

• Microglial (CNS)

• Ependymal cells (CNS)

• Oligodendrocytes (CNS)

• Satellite cells (PNS)

• Schwann cells (PNS)

Astrocytes

• Most abundant, versatile, and highly branched glial cells

• Cling to neurons, synaptic endings, and capillaries

• Functions include

  • 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

Microglial cells

• Small, ovoid cells with thorny process that touch and monitor neurons

• Migrate toward injured neurons

• Can transform to phagocytize microorganisms and neuronal debris

Ependymal cells

• Range in shape from squamous to columnar

• May be ciliated

  • Cilia beat to circulate CSF

• Line the central cavities of the brain and spinal column

• Form permeable barrier between cerebrospinal fluid (CSF) in cavities and tissue fluid bathing CNS cells

Oligodendrocytes

• Branched cells

• Processes wrap CNS nerve fibers, forming insulating myelin sheaths thicker nerve fibers

• Satellite cells

• Surround neuron cell bodies in PNS

• Function similar to astrocytes of CNS

• Schwann cells (neurolemmocytes)

• Surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers

  • Similar function as oligodendrocytes

• Vital to regeneration of damaged peripheral nerve fibers

Neurons

• Structural units of nervous system

• Large, highly specialized cells that conduct impulses

• Extreme longevity (-> 100 years or more)

• Amitotic (direct cell division; usually without spindle formation or visible chromosomes) with few exceptions

• High metabolic rate - requires continuous supply of oxygen and glucose

• All have cell body and one or more processes

• Amitotic

(direct cell division; usually without spindle formation or visible chromosomes

Neuron cell body (perikaryon or soma)

• Biosynthetic center of neuron

  • Synthesizes proteins, membranes, and other chemicals

  • Rough ER (chromatophilic substance or nissl bodies)

    • Most active and best developed in body

• Spherical nucleus with nucleolus

• Some contain pigments

• In most, plasma membrane part of receptive region

• Most neuron cell bodies in CNS

  • Nuclei - clusters of neuron cell bodies in CNS

• Ganglia - lie along nerves in PNS

• Ganglia

• lie along nerves in PNS

Neuron processes

• Armlike processes extend from body

• CNS

  • Both neuron cell bodies and their processes

• PNS

  • Chiefly neuron processes

• Tracts

  • Bundles of neuron processes in CNS

• Nerves 

  • Bundles of neuron processes in PNS

• 2 types of processes

  • Dendrites

  • Axon

• Tracts

• Bundles of neuron processes in CNS

Dendrites

• In motor neurons

  • 100s of short, tapering, diffusely branched processes

  • Same organelles as in body

• Receptive (input) region of neuron

• Convey incoming messages toward cell body as graded potential (short distance signals)

• In many brain areas fine dendrites specialized

  • Collect information with dendritic spines

    • Appendages with bulbous or spiky ends

Axon: structure

• One axon per cell

• In some axon short or absent

• In others most of length of cell

  • Some 1 meter long

• Long axons called nerve fibers

Axon: functional characteristics

• Conducting region of neuron

• Generates nerve impulses

  • Neurotransmitters released into extracellular space 

    • Either excite or inhibit neurons with which axons in close contact

• Carriers on many conservations with different neurons at the same time

• Lacks rough ER and golgi apparatus

  • Relies on cell body to renew proteins and membranes

  • Efficient transport mechanisms

  • Quickly decay if cut or damaged

Myelin sheath

• Composed of myelin

  • Whitish, protein-lipiod substance

• Segmented sheath around most long or large-diameter axons

  • Myelinated fibers

• Function of myelin

  • Protects and electrically insulates axon

  • Increases speed of nerve impulse transmission

• Unmyelinated fibers conduct impulses more slowly

• Function of myelin

• Protects and electrically insulates axon

• Increases speed of nerve impulse transmission

Myelination in the PNS

• Formed by schawann cells

  • Wrap around axon in jelly roll fashion

  • One cell forms one segment of myelin sheath

• Myelin sheath

  • Concentric layers of schwann cell plasma membrane around axon

Myelin sheaths in the CNS

• Formed by multiple, flat processes of oligodendrocytes, not whole cells

• Can wrap up to 60 axons at once

• Nodes of ranvier are present 

• No outer collar of perinuclear cytoplasm

• Thinnest fibers are unmyelinated

  • Covered by long extensions of adjacent neuroglia

• White matter

  • Regions of brain and spinal cord with dense collections of myelinated fibers - usually fiber tracts

• Gray matter

  • Mostly neuron cell bodies and unmyelinated fibers

  • specialized tissue of the central nervous system (CNS) responsible for processing and interpreting information

• White matter

• Regions of brain and spinal cord with dense collections of myelinated fibers - usually fiber tracts

• Gray matter

• Mostly neuron cell bodies and unmyelinated fibers

• specialized tissue of the central nervous system (CNS) responsible for processing and interpreting information

Motor division of PNS: somatic nervous system

• Somatic motor nerve fibers

• Conducts impulses from CNS to skeletal muscle

• Voluntary nervous system

  • Conscious control of skeletal muscles

Membrane Potential changes used as communication signals

• Membrane potential changes when 

  • Concentrations of ions across membrane change

  • Membrane permeability of ions changes

• Changes in membrane potential used as signals to receive, integrate, and send information

The synapse

• Nervous system works because information flows from neuron to neuron

• Neurons functionally connected by synapses

  • Junctions that mediate information transfer

    • From one neuron to another neuron

    • Or from one neuron to an effector cell

Varieties of synapses: electrical synapses

• Less common than chemical synapses

  • Neurons electrically coupled (joined by gap junctions that connect cytoplasm of adjacent neurons)

    • Communication very rapid

    • May be unidirectional (eyes and ears) or bidirectional (the brain sends signals to the muscles and the muscle sends a signal to the brain by moving)

    • Synchronize activity

  • More abundant in:

    • Embryonic nervous tissue

• Nerve impulse remains electrical

Varieties of synapses: chemical synapses

• Specialized for release and reception of chemical neurotransmitters (ACh - in our muscle)

• Typically composed of two parts

  • Axon terminal of presynaptic neuron

    • Contains synaptic vesicles filled with neuro transmitter

  • Neurotransmitter receptor region of postsynaptic neuron’s membranes

    • Usually on dendrite or cell body

• 2 parts separated by synaptic cleft

  • Synaptic cleft: Fluid-filled space where an electrical signal from one neuron is converted into a chemical message to communicate with the next cell

• Electrical impulse changed to chemical across synapse, then back into electrical

• Synaptic cleft

• Fluid-filled space where an electrical signal from one neuron is converted into a chemical message to communicate with the next cell

Termination of neurotransmitter effects

• Within a few milliseconds neurotransmitter effect terminated in one of three ways

  • Reuptake

    • By astrocytes or axon terminal

  • Degradation

    • By enzymes

  • Diffusion

    • Away from synaptic cleft

Neurotransmitters

• Language of nervous system

• 50 or more neurotransmitters have been identified

• Most neurons make 2 or more neurotransmitters

  • Neurons can exert several influences

• Usually released at different stimulation frequencies

• Classified by chemical structure and by function

Melatonin

the brain's "night shift" signal, primarily responsible for regulating your sleep-wake cycle (circadian rhythm)

• Acetylcholine (Ach)

• First identified; best understood

• Released at neuromuscular junction, by some ANS neurons, by some CNS neurons

• Synthesized by acetic and choline by enzyme choline acetyltransferase

• Degraded by enzyme acetylcholinesterase (AChE)

• Aids in memory formation

• Less produced as Alzheimer's progresses

• Biogenic amines

• Catecholamines

  • Dopamine, norepinephrine (NE), and epinephrine

  • Norepinephrine: a chemical transmitter and hormone that triggers the fight or flight response

  • Epinephrine: a hormone and neurotransmitter that acts as the body’s ultimate emergency signal; adrenaline

  • Dopamine: the brain’s primary chemical for reward, motivation, and movement; creates a reward or pleasure signal

  • Synthesized from amino acid tyrosine

• Indolamines

  • Serotonin and histamine

  • Serotonin 

    • synthesized from amino acid tryptophan

    • the brain’s primary "mood stabilizer" and regulator of essential body functions

  • Histamine 

    • synthesized from amino acid histidine

    • the body’s "first responder" for inflammation, allergies, and wakefulness

  • Serotonin synthesized from amino acid tryptophan; histamine synthesized from amino acid histidine

• Broadly distributed in brain

  • Play roles in emotional behaviors and biological clock

• Some ANS motor neurons (especially NE)

• Imbalances associated with mental illness

• Catecholamines

• Dopamine, norepinephrine (NE), and epinephrine

• Synthesized from amino acid tyrosine

Indolamines

• Serotonin and histamine

• Serotonin synthesized from amino acid tryptophan; histamine synthesized from amino acid histidine

Norepinephrine

a chemical transmitter and hormone that triggers the fight or flight response

Epinephrine

a hormone and neurotransmitter that acts as the body’s ultimate emergency signal; adrenaline

Dopamine

the brain’s primary chemical for reward, motivation, and movement; creates a reward or pleasure signal

Serotonin

• synthesized from amino acid tryptophan

• the brain’s primary "mood stabilizer" and regulator of essential body functions

Histamine

• synthesized from amino acid histidine

• the body’s "first responder" for inflammation, allergies, and wakefulness

• Amino acids

• Glutamate

• Aspartate

• Glycine

• GABA – gamma (y)-aminobutyric acid

• Peptides (neuropeptides)

• Substance P

  • Mediator of pain signals

• Endorphins

  • Act as natural opiates; reduce pain perception

• Endorphins

• Act as natural opiates; reduce pain perception

• Gases and lipids - gasotransmitters

• Nitric oxide (NO)

  • NO involved in learning and formation of new memories; brain damage in stroke patients, smooth muscle relaxation in intestine

• Carbon monoxide (CO)

• Bind with G protein-coupled receptors in the brain

• Nitric oxide (NO)

• NO involved in learning and formation of new memories; brain damage in stroke patients, smooth muscle relaxation in intestine

• Endocannabinoids

• Act at same receptors as THC (active ingredient in marijuana (used to help with chemo))

  • Most common G protein-linked receptors in brain

• Lipid soluble

• Synthesized on demand

• Believed involved in learning and memory

• May be involved in neuronal development, controlling appetite, and suppressing nausea

Classification of neurotransmitters: function

• Great diversity of functions

• Can classify by

  • Effects - excitatory vs inhibitory

  • Actions - direct vs indirect

• Effects - excitatory vs inhibitory

  • Neurotransmitter effects can be excitatory (depolarizing) and/or inhibitory (hyperpolarizing)

  • Effect determined by receptor to which it binds

  • GABA and glycine usually inhibitory

  • Glutamate usually excitatory

  • Acetylcholine and NE bind to at least 2 receptor types with opposite effects

    • ACh excitatory at neuromuscular junctions in skeletal muscle

    • ACh inhibitory in cardiac muscle

• Effects

• Effects - excitatory vs inhibitory

• Actions - direct vs indirect

• Effects - excitatory vs inhibitory

  • Neurotransmitter effects can be excitatory (depolarizing) and/or inhibitory (hyperpolarizing)

  • Effect determined by receptor to which it binds

  • GABA and glycine usually inhibitory

  • Glutamate usually excitatory

  • Acetylcholine and NE bind to at least 2 receptor types with opposite effects

    • ACh excitatory at neuromuscular junctions in skeletal muscle

    • ACh inhibitory in cardiac muscle

• Actions

 direct vs indirect

Central nervous system (CNS)

• CNS consists of brain and spinal 

• Cephalization

  • Evolutionary development of rostral (anterior) portion of CNS

  • Increased number of neurons in head

  • Highest level reached in human brain

Cephalization

• Evolutionary development of rostral (anterior) portion of CNS

• Increased number of neurons in head

• Highest level reached in human brain

• Adult brain regions

• 1. Cerebral hemispheres (cerebrum)

• 2. Diencephalon (thalamus, hypothalamus)

• 3. Brain stem (midbrain, pons, and medulla)

• 4. Cerebellum

• Spinal cord

• Central city surrounded by gray matter

• External white matter composed of myelinated fiber tracts

Brain

• Similar pattern

• Additional areas of gray matter in brain

• Cerebral hemispheres and cerebellum

  • Outer gray matter called cortex

• Cortex disappears in brain stem 

  • Scattered gray matter nuclei amid white matter

Ventricles of the brain

• Spaces filled with cerebrospinal fluid (CSF)

• Lined by ependymal cells

• Connected to one another and to central canal of spinal cord

• Surface markings

• Ridges (gyri), shallow grooves (sulci), and deep grooves (fissures)

• longitudinal fissure

  • Separates two hemispheres

• Transverse cerebral fissure

  • Separates cerebrum and cerebellum

• longitudinal fissure

• Separates two hemispheres

• Five lobes

frontal, parietal, temporal, occipital, insula

Frontal lobe

• planning, decision making, problem solving, and organizing; motor control, personality and speech production

  • Includes primary motor, premotor, frontal eye field, prefrontal and broca’s area

Parietal lobe

• interprets touch, pain, pressure, and temperature; spatial awareness, and mathematical processing

  • Includes: primary somatosensory and somatosensory association

Temporal lobe

• hearing, language comprehension, memory and recognition

  • Includes wernicke’s area, primary auditory, and auditory association

occipital lobe

• visual perception, processing details, and visual memory

  • Includes: primary visual and visual association

insula

bridge between your body’s physical sensations and emotions. It handles interoception, emotional awareness, pain, taste, and addiction

Central sulcus

• Separates precentral gyrus of frontal lobe and postcentral gyrus of parietal lobe

• Parieto-occipital sulcus

• Separates occipital and parietal lobes

Lateral sulcus outlines

•  temporal lobes

• 3 basic regions

• Cerebral cortex of gray matter superficially

• White matter internally

• Basal nuclei deep within white matter

Cerebral cortex

• Thin (2-4 mm) superficial layer of gray matter

• 40% mass of brain

• Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding

• Makes your personality

4 general considerations of cerebral cortex

• 1. 3 types of functional areas

  • Motor areas-control voluntary movement (skeletal muscles)

  • Sensory areas - conscious awareness of sensations

  • Association areas - integrate diverse information with something you have seen/heard/smelled before

• 2. Each hemisphere concerned with contralateral side of body (controls the opposite side of the body) 

• 3. Lateralization of cortical function in hemispheres

• 4. Conscious behavior involved entire cortex in some way

• Motor areas

control voluntary movement (skeletal muscles)

• Sensory areas

conscious awareness of sensations

Association areas

integrate diverse information with something you have seen/heard/smelled before

Motor areas of cerebral cortex

• In frontal lobe; control voluntary movement

• Primary (somatic) motor cortex in precentral gyrus

• Premotor cortex anterior to precentral gyrus

• Broca’s area anterior to inferior premotor area

• Front eye field within and anterior to premotor cortex; superior to Broca’s area

Gyrus

• The ridges

• Increases brains surface area for more neurons and higher cognitive processing power 

• Precentral gyrus: 

  • The front gyrus

  • Posterior part of the Frontal Lobe, just in front of the central sulcus.

  • Function: motor Control - houses the primary motor cortex; controls voluntary muscle movements on the opposite side of the body

• Postcentral Gyrus:

  • Anterior part of the Parietal Lobe, just behind the central sulcus.

  • Function: Sense of Touch - houses the primary somatosensory cortex; processes touch, pressure, pain, temperature, and body position.

• Precentral gyrus: 

• The front gyrus

• Posterior part of the Frontal Lobe, just in front of the central sulcus.

• Function: motor Control - houses the primary motor cortex; controls voluntary muscle movements on the opposite side of the body

• Postcentral Gyrus:

• Anterior part of the Parietal Lobe, just behind the central sulcus.

• Function: Sense of Touch - houses the primary somatosensory cortex; processes touch, pressure, pain, temperature, and body position.

Sulcus

• The valleys that everyone has

• Increases brains surface area so more neurons can fit in the skull

• Central sulcus

  • Separates precentral gyrus of frontal lobe and postcentral gyrus of parietal lobe

• Parieto-occipital sulcus

  • Separates occipital and parietal lobes

• Lateral sulcus outlines temporal lobes

Fissures

• Deep, prominent groove or cleft that divides the brain into large, distinct regions or lobes

Primary areas

• Function: Handle basic input/output (sensory or motor)

• Examples: Primary motor cortex (movement), primary sensory cortex (touch)

• Key idea: First to receive or send signals

Association areas

• Function: Process and interpret information

• Examples: Thinking, memory, decision-making

• Key idea: Make sense of information and connect it together

Primary motor cortex

• Allows conscious control of precise, skilled, skeletal muscle movements

Premotor cortex

• Helps plan movements; staging area for skilled motor activities

• Controls learned, repetitious, or patterned motor skills (like running, walking, and writing)

• Coordinates simultaneous or sequential actions

• Controls voluntary actions that depend on sensory feedback