Physl 210A 2nd part

Cell types of nervous system

• Neurons

• Glial

  • Astrocytes

  • Oligodendrocytes

  • Ependymal cells

  • Microglia

Neurons

Functional unit of the nervous system

• generate action potentials

• Interconnected information processors essential for all tasks of nervous system

Glial cells

Non-neuronal cells that support neurons physically and metabolically

• do not generate action potentials

• Provide scaffolding to have neurons line up closely with one another

• Neuronal communication, transport nutrients and waste, mediate immune response, and insulation to neurons

Nerve

Bundle of axons or fibres that travel together

• does not contain a complete nerve cell — only the axonal portion of many neurons

• Individual fibres within this do not have any influence on one another — just follow the same pathway

Central nervous system

Integrating and command center

• brain and spinal cord

Peripheral nervous system

Nerves connecting brain to peripheral structures

• Afferent

  • Somatic sensory

  • Visceral sensory

  • Special sensory

• Efferent

  • Somatic motor

  • Autonomic motor

Somatic sensory

Spatial limits of body

Visceral sensory

Information on internal organs

Special sensory

Sight, hear, equilibrium, taste, smell

Somatic motor

Skeletal muscle movement divided into

• Reflexes

• Rhythmic motor behaviours

• Voluntary

Autonomic motor

• Effects

  • smooth muscle

  • Cardiac muscle

  • Glands

• Systems

  • Sympathetic

  • Parasympathetic

  • Enteric

• Involuntary

Ganglion

Collection of cell bodies located outside the CNS

Astrocytes

• physically support neurons - scaffolding

• Form blood brain barrier

• Repairing

  • Form scar tissue → inhibits regeneration of severed axons

• Turnover/recycle neurotransmitter molecules

• Maintain electrolytic balance

  • Na+, K+, Ca2+, H+ (pH)

Oligodendrocytes

Form myelin sheaths that electrically insulate axons

• have few branches

Ependymal cells

Produce cerebrospinal fluid (CSF)

Microglia

Ingest bacteria and debris

CNS gray matter

Consists of unmyleinated nerve cell bodies, dendrites, and axon terminals

• cell bodies in organized fashion

• Nuclei

Nuclei

Clusters of cell bodies in brain and spinal cord with similar functions → identified by specific names

CNS White matter

Mostly myelinated axons and very few cell bodies

• myelin sheath gives colour

• Tracts

• Neural tissue?

Tracts

Bundle of axons that connect different regions of the CNS

• same as nerves in PNS

Neural tissue

Have minimal extracellular matrix and must rely on external support for protection of trauma

• outer casing of bone

• 3 layers of connective tissue membrane

• Fluid between membranes

Protective elements of CNS

• Bone

  • Skull → brain

  • Vertebrae → spinal cord

• Meninges

• Cerebrospinal fluid

• Blood brain barrier

Meninges

3 layers of membrane that lie between bone and CNS to help stabilize neural tissue and protect from bruising against bones of skeleton

• dura mater

• Arachnoid mater

• Pia mater

Cerebrospinal fluid

Provides physical and chemical protection

• in specific spaces of the brain

• Continuously secreted from brain ventricles by choroid plexus

• Reabsorbed by special villi (in arachnoid membrane) into venous blood after flowing around neural tissue

  • Same rate as produced

• Provides mechanical protection

  • Bathes and supports neural tissue

  • fluid compresses before brain hits cranium

• Maintains electrolyte balance around neurons

Blood brain barrier

helps maintain a stable environment for the brain

• capillaries are less porous → allow small molecules in

  • Protection from chemical fluctuations and harmful agents

• Provides oxygen and glucose and selectively transports molecules via carrier mediated transport

• Drugs must be precursors (small enough to pass)

Regular capillaries

Have passages between cells that make up walls that allow fluid with electrolytes and large molecules and white blood cells to exit from interior

• porous

Dura mater

Tough outer layer part of meninges

• like Saran wrap

Arachnoid mater

Spidery intermediary mesh part of meninges

• loosely tied with Pia mater

Subarachnoid space

The space between arachnoid and Pia mater in the meninges

Pia mater

Delicate inner layer of the meninges

• adheres to surface of brain and spinal cord

Meningitis

Infection of the meninges

Hydrocephalus

occurs when reabsorption is blocked and CSF accumulates

• Treated with drainage tubes

  • If not— brain tissue is crushed against inner surface of skull

• Creates pressure in cavities of CNS → ventricles and spinal central canal

Brain planes (visuals)

• coronal or frontal plane

  • Front/back sections

• Sagittal plane

  • Left/right

• Horizontal or transverse plaNe

  • Up/down

Directions - long axis of body

Straight line in body

• superior (above)

• Posterior (behind)

• Inferior (below)

• Anterior (in front of)

Connects with axial CNS at a 120 degree angel in midbrain

Directions - long axis of CNS

Bent — cephalic flexure

• dorsal

  • Hindbrain: back

  • Forebrain: top of head

• Ventral

  • Hindbrain: front

  • Forebrain: towards gut

• Rostal

  • Hindbrain: front aspect of head (top)

  • Forebrain: nasal region

• Caudal

  • Hindbrain: tail region

  • Forebrain: posterior (back) of head

Connects with axial body at a 120 degree angel in midbrain

Brain 3 main regions

• Cerebrum

• Cerebellum

• Brain stem

Forebrain

• cerebrum

• Diencephalon

Hindbrain

• cerebellum

• Pons

• Medulla oblongata

Brain stem

• midbrain

• Pons

• Medulla oblongata

Functions

• Respiration, locomotion, cardiovascular, neurotransmitter supply

• Cardiovascular, blood vessel, digestive

• Sleep/wake cycle

• Balance and posture

Neurotransmitter produced in brain stem are transported along axons to other parts of brain

Central Nervous System formation

During development

• forms from a long tube

  • Lumen of the tube remains in adult brain as fluid filled space (ventricular system)

    • Filled with CSF

  • Brain formed from walls of the tube → increasing complexity

Cerebrum

• Includes

  • corpus callosum

  • Cerebral cortex

Corpus callosum

Large bundle of nerves; connects right and left hemispheres

• ensures communication and cooperation

Cerebral cortex

The outer layer of neural tissue of cerebrum of the brain; folded into peaks and grooves

• thin outer shell of grey matter

• Neurons arranged in anatomically distinct horizontal layers and functionally distinct vertical layers

Functions:

• sensory perception

• Motor control

• Language

• Cognitive functions

Sulci

Groove in the brain

Gyri

Fold/ridge in the brain

Bones of the skull

22 bones

• 8 cranium

• 14 facial

8 cranium bones that enclose the brain

• Frontal bone

• 2 parietal bones

• 2 temporal bones

• Occipital bone

• Sphenoid bone

• Ethmoid bone

Diencephalon

The region of embryonic vertebrae neural tube that gives rise to anterior forebrain structure

• encloses the third ventricle cavity

• Includes

  • Thalamus

  • Epithalamus

  • Hypothalamus

  • Subthalamus

Thalamus

Integrating center and relay station for sensory and motor information

• projects fibres to cerebrum

• Almost all sensory information

• Can shape sensory information

Functions:

• sensory switchboard which selects and relays sensory signal to cerebral cortex

• Skeletal muscle contraction

• Awareness

Epithalamus

Includes pineal gland

• part of Diencephalon

Pineal gland

Melatonin secretion

Hypothalamus

Homeostasis and behavioural drives

• temperature control, water balance, hunger

• Fight or flight or fright

• includes posterior pituitary

• integration and command center for autonomic functions; temperature regulation

Posterior pituitary

Hormone secretion

Subthalamus

Movement regulation

Midbrain

AKA mesenophalon

• eye movement

• Auditory and visual processing

• Contains the substantia nigra

• Has different neuron clusters and pathways and other structures 

Substantia nigra

Rich in dopamine neurons and part of basal ganglia

• divided into 2 regions

  • Pars reticular a

  • Pars compacta

Basal ganglia

• Group of 5 nuclei associated with motor and learning functions (paired) deep within cerebral cortex

• Received input from context and provides feedback to context (thalamus) for development of motor strategies and regulation of movement 

  • Initiate movement

  • Suppressing activity of muscles to inhibit movement 

• Forms major portion of extrapyramidal system

• Looping parallel circuits regulate motor activity — circuits allow signals to travel sensorimotor cortex → basal nuclei → thalamus → context → modulate movement 

Pons

• Relay station between cerebrum and cerebellum

• Coordination of breathing with medulla

Medulla oblongata 

• control of involuntary function

  • Autonomic centers for regulation of visceral functions

    • Cardiovascular, respiratory, digestive activities

• Connects brain stem to spinal cord

• contains major ANS reflex centers (centers for cardiovascular, respiratory, digestive activity)

Frontal section of forebrain 

• outer shell of gray matter composed of cell bodies 

• Inner layer of white mater composed of tracts of myelinated axons

• 6 layers of cerebral cortex

  • Distinct cells based on physical properties and inputs/outputs

  • Parallel to cortical surface

    • Numbered from outer to inner membrane

• Corpus callosum 

Limbic system 

A ring of forebrain structures that surround the brain stem and are interconnected by intricate neuron pathways

• learning, emotion, appetite (visceral function), sex, endocrine integration, behavioural and emotional responses

  • Especially for survival

• Also connects to CNS

• Includes

  • Thalamus

  • Hypothalamus

  • Basal ganglia

  • Cingulate gyrus

  • Hippocampus

  • Amygdala

Cerebellum

• Influences posture and movement indirectly by means of input to brainstem nuclei and by way of thalamus to regions of sensory motor cortex that give rise to pathways that descend to motor neurons

• Receives input from sensorimotor and vestibular system (eyes, skin, muscles, joints, tendons — movement effects these receptors)

• Inputs

  • Sensory input from spinal cord

  • Motor commands from cerebral cortex

• Functions

  • Motor timing, scaling, coordination and learning

    • Trunk/neck, arms/hands/fingers

  • Balance and gait

  • Eye movements

  • Hints at cognitive processing

Frontal lobe 

• Personality, emotion

• Motor control

Parietal lobe

Somatosensation

Occipital lobe

Vision

Temporal lobe

Hearing and memory

Spinal cord

Major pathway of information, flowing back and forth between the skin, joints, and muscles of the body

• 31 spinal nerves convey signal to and from spinal cord

• Ascending sensory axons which transmit sensory information from body to brain

• Descending axons that control movement and autonomic functions

• Locomotor pattern generator (producing rhythmic movements)

  • Spinal reflexes

• integrates autonomic reflexes (Urination, defecation); brain is able to influence these reflexes

Spinal nerve

Innervates a specific area of the skin and a specific set of muscles

• one member of pair exists of right side and left side of spinal column separately  

• Contains afferent and efferent nerves

• 31 pairs that connect to spinal cord

• Arise at cervical, thoracic, lumbar, sacral, causageal region of spinal cord

Dermatome

Specific area of the skin innervated by a single spinal nerve root — supplied by a pair of spinal nerves

Myotome

Specific set of muscles innervated by a single spinal nerve root — supplied by a pair of spinal nerves 

Shingles 

Neurons in the dorsal root ganglia, often in 1 or 2 segments, become infected with virus related to chicken pox.

• bands of sores and pains

• chicken pox in children increases likelihood of this in adulthood

  • Dormant → mutates and activates 

• knowledge of dermatones used to clinically determine level of spinal cord and injury

Functions of the Spinal cord

• sends sensory information from the body to the brain (dorsal root)

  • Spinal interneurons may route sensory information to the brain through ascending tracts

• Sends motor commands from the brain to the body (ventral root)

• Coordinate reflexes (acting without signals from the brain)

• Also contains central pattern generators that control rhythmic movement

  • Can be modulated with or without information from higher brain centers

Interface between PNS and CNS

1. Sensory afferents enter spinal cord via dorsal root

2. Sensory afferents bifurcate into ascending / descending axons.

   1. Ascending forms dorsal root columns → ascend into brainstem → sensory information to the brain

3. Descending branch travels causally for 2-3 spinal segments

4. Every mm or so for 2-3 segments (50mm humans) the ascending/descending axons send branches into the gray matter of the spinal cord which synapse in the interneurons and motor neurons 

5. Motor neuron cell bodies are located in ventral horn

6. Motor efferent axons leave spinal cord and form ventral root 

Cervical C1-C8

Head, neck, shoulders, arm, hand 

Thoracic T1-T12

Trunk

Lumbar L1-L5

Waist, front of legs, feet 

Sacral S1-S5 and Coccygeal

Buttocks, genitals, anus, back of legs, feet

Spinal cord gray matter

Neuronal cell bodies and their dendrites, short interneurons, glial cells 

Spinal cord horn

Projection of gray matter towards outer surface of the spinal cord

• dorsal/posterior — interneuron cell bodies

• Ventral/anterior — motor neuron cell bodies

• Lateral — autonomic neuron cell bodies

Dorsal roots

Dorsal side of the cord where axons of afferent neurons enter the spinal cord

Dorsal root ganglia 

Contain the cell bodies of the afferent neurons (the swelling)

Ventral roots

The ventral side of the cord where axons of efferent neurons leave the spinal cord

Ganglia 

Group of neuronal cell bodies located outside the central nervous system in the peripheral nervous system

Spinal cord white matter

Surrounds gray matter

• consists of bundles of axons (with myelin) that travel up and down the spinal cord and convey sensory signals ascending to brain (cord to brain) or motor commands descending from brain (brain to cord)

• Funiculi — three pairs of white matter bundles

  • Posterior/dorsal, lateral, anterior/ventral

• Tracts/fasiciuli

  • Ascending/sensory

  • Descending/motor

Funiculi 

bundles of nerve fibers (axons) in the spinal cord's white matter

Fasciculi

groups of short fibres, ascending and descending, and crossed and uncrossed, within the spinal cord

• tracts —subdivisions of each column 

Spinal reflex

Simple behaviour produced by central nervous system pathways that lie entirely within spinal cord

• afferent sensory fibres envole reflexes → enter spinal cord and activate spinal interneurons directly or through a chain of one or more spinal interneurons

• Pathways may be affected by descending pathways from brain either directly or through other spinal interneurons

  • Short term and long term influence over spinal cord reflex

Short term influence over spinal cord reflex 

The brain rapidly adjusts spinal reflexes to suit the needs of different tasks

Long term influence over spinal cord reflex 

Gradually shapes spinal reflexes during development, skill acquisition, later in life, and in response to CNS trauma and disease

Spinal cord injury

Sensation from and the motor control of functions below that level (of transection) are likely to be abnormal depending on severity

Tretaplegia/quadraplegia

the paralysis of all four limbs, the trunk, and pelvic organs, typically caused by a high-level spinal cord or brain injury

Paraplegia

the inability to voluntarily move the lower parts of the body— lower level spinal cord injury

Specializations of cerebral cortex

• Sensory areas

• Motor areas

• Association areas

Cerebral cortex — sensory areas

Sensory input translated into perception (awareness) in cerebral cortex

• all cortical areas associated with sensory

• Receiving and interpreting — transduction

• Includes

  • Gustatory cortex — taste

  • Primary olfactory cortex — smell

  • Pimraru somatic sensory cortex — parietal lobe

  • Visual cortex — vision

  • Auditory cortex — hearing

Cerebral cortex — motor areas

Plan, control, and execute voluntary movements in cerebral cortex

Cerebral cortex — association areas

Integrate information from sensory and motor areas in cerebral cortex

• general visual, auditory, gustatory

Somatic senses

Receptors associated with the skin, muscles, joints, fascia, and viscera

• somatosensory

Special senses

Include the senses of smell, taste, hearing, static equilibrium, dynamic equilibrium, and sight 

Somatosensory system

Part of sensory system concerned with the conscious perception of touch, pressure, pain, temperature, position, movement and vibration detected by receptors in the skin, muscles, joints, fascia, and viscera

• relays sensations detected in the periphery and conveys them via pathways through the spinal cord, brainstem, and thalamic relay nuclei to sensory cortex in the parietal lobe 

Sensory pathways

Stimulus (interna/external) → sensory receptor that transduces stimulus into electrical graded potentials → reach threshold → action potentials travel along afferent sensory neuron to CNS → signals integrated

• some stimuli pass upwards to cerebral cortex → reach conscious perception

• Some acted upon without our awareness — does not reach brain

• At each synapse along the way —nervous system can module and shape information

• Primary sensory (first order) neuron → secondary sensory (second order) neuron → etc etc

• Divided into 2 systems

  • Below neck — pass along sensory pathway of spinal cord (ascending pathway)

  • Head and neck — travel through cranial nerves

• Sensory information from spinal cord → brainstem → sensory areas of cerebrum 

  • Pathways pass through thalamus to cerebral cortex except olfactory