Neurophysiology - CNS, PNS, CSF, BBB Flashcards
What are the 2 subdivisions of the CNS?
Brain
Spinal Cord
Functions of brain
Receive and process sensory information
Initiate responses
Store memories
Generate thoughts and emotions
Functions of spinal cord
Conduct signals to and from brain
Control reflex activities
What are the 2 main subdivisions of the PNS?
Sensory (afferent) (visceral and somatic)
Motor (efferent) (visceral and somatic)
Function of sensory (afferent) division
Bring info from receptors to CNS
Functions of visceral sensory division
Provide info about internal organs via visceral receptors and sensory neurons
Functions of somatic sensory division
Provide info about position, touch, pressure and pain via somatic receptors and sensory neurons
Function of motor (efferent) division
Carry motor commands from CNS to peripheral tissues and systems.
Functions of visceral motor division
*2 subdivisions
Autonomic regulation of smooth and cardiac muscle, glands, and adipose tissue.
Sympathetic (fight or flight)
Parasympathetic (rest and digest)
Function of somatic motor division
Control skeletal muscle contractions (voluntary)
Parts of a neuron (7)
- Dendrites - receive info
- Cell body (soma) - contains oraganelles
- Axon - ext of cell membrane, carries info
- Axon Hillock/Trigger Zone - axon origin, AP origin
- Presynaptic Terminal - transmits info
- Myelin Sheath - increases transfer speed
- Nodes of Ranvier - Gaps in myelin sheath
Structural classifications of neurons (4)
- Multipolar - most common - 1 axon, many dendrites
- Bipolar - 2 processes (1 axon, 1 dendrite)
- Pseudounipolar - single stem process that bifurcates to form 2 processes (1 to PNS, 1 to CNS)
- Unipolar - dendrites and axon stem from a single process. Common in insects
Functional classifications of neurons (3)
- Sensory - most pseudounipolar, send info from receptors toward CNS
- Interneurons (association) -multi or bipolar, in CNS, connect sensory and motor neurons.
- Motor - multipolar, send info from CNS to muscles/glands (effector organs)
Types of Glial cells (5)
- Microglial cells (CNS)
- Astrocytes (CNS)
- Oligodendrocytes (CNS)
- Ependymal cells (CNS)
- Schwann cells (PNS)
Astrocyte functions
Star shaped w/ long processes.
Structural and metabolic support for neurons
form inner and outer glial limiting membrane
neurotrophic (neuronal survival)
elongate axons/dendrites
tissue repair
neuron communication
control neurotrans around synapse.
Oligodendrocyte functions
Support to axons of neurons in CNS
Processes to form myelin
Myelinate most axons > 1um diameter
Ependymal cell functions
Cover ventricles of brain, central canal and choroid plexus.
Involved in creating CSF.
Schwann cell functions
(neurolemmocytes).
Support axons of neurons in PNS (similar to oligodendrocytes).
Each cell forms internodes of myelin sheath.
Major functional areas of the brain (5)
- Cerebrum (telencephalon)
- Cerebellum
- Thalamus
- Hypothalamus
- Brainstem
Functions of cerebrum
Role in conscious experience of sensation and initiation of voluntary movement.
Functions of cerebellum
Role in synchronizing muscle activity and controlling equilibrium and eye movement.
Works with vestibular system.
Damage to cerebellum causes:
Loss of spatial accuracy and smooth execution of movement.
Loss of equilibrium.
Functions of thalamus
Pre-processes all info reaching the cerebral cortex.
Extends into cerebral hemisphere; gateway to cortex.
Essential for consciousness, attention, and alertness.
What’s up with the limbic system?
Found at border between cerebrum and thalamus, the limbic system is a circuit that relates to behavior, arousal, emotions, and memory. It’s also related to the autonomic NS, which is why your emotions can affect visceral functions (HR, BP, GI motility)
Functions of hypothalamus
Homeostasis.
Remember the 4 F’s (fighting, fleeing, feeding, and sex).
Neurological and endocrine connection.
Secretes releasing and inhibitory hormones that control anterior pituitary secretion.
Sections of brainstem (3)
- Medulla - HR, BP, breathing, circadian, swallowing (autonomous). End of stem.
- Pons - maintain consciousness and alertness. Influence posture, locomotion and visceral funct. Pathway to relay sensory info between cerebellum and cortex. Middle of stem.
- Midbrain - location of brainstem UMN pathways. Extrapyramidal tracts. Subconscious posture and voluntary learned movements. Top of stem.
What is gray matter?
Nerve cell bodies and their processes. (cerebral cortex). Where all the synapses are.
What is white matter?
Myelinated axons that connect different parts of gray matter to each other.
Functional areas of the cerebral cortex (3)
- Motor
- Sensory
- Association
Function of sensory cortex
Receive sensory signals from brainstem and spinal cord.
Somatosensory, visual, auditory, vestibular, olfactory.
Function of motor cortex
Voluntary movement.
Corticospinal/pyramidal tract: primary motor area - muscle activation
Premotor frontal cortex - plan and organize movement
Supplementary motor - preparatory orientation of the body to execute task
Function of association cortex
learning and intelligent behavior. Integrate sensory, memory, and behavior centers.
What’s up with basal nuclei?
Gray matter nuclei within white matter of cerebral cortex. Help select appropriate movement pattern while suppressing less appropriate ones (inhibitory output). Inhibition by dopamine-containing neurons (degenertion = Parkinson’s).
Microglial cell functions
Brain immune cells.
Act as macrophages, clear debris by phagocytosis.
Release NO to prevent viral infection.
Role in developing brain - destroy unnecessary synapses.
Fibers in dorsal root of spinal cord
sensory
Fibers in intermediate horn of spinal cord
autonomic (not in lumbar)
Fibers in ventral root of spinal cord
motor
Where do the cord reflexes originate?
Cord gray matter, through dorsal horn. Signals travel to 2 locations; the gray matter for local reflexes, and then higher levels of the cord, brainstem, or cerebral cortex.
What are the main components of a spinal nerve? (3)
- Roots (dorsal and ventral)
- Main trunk
- Peripheral branches
What are the 4 types of fibers in spinal nerves?
- Somatic sensory - enter cord through dorsal roots from skin, muscle
- Visceral sensory - enter cord through dorsal roots from thoracic and abdominal organs, olfactory epithelium, taste buds.
- Somatic motor - leave cord through ventral root. Go to skeletal muscle.
- Visceral motor - leave cord through ventral horn. Go to smooth/cardiac muscle, glands.
What are the 3 meninges?
- Dura Mater
- Arachnoid
- Pia Mater
Characteristics of the Dura Mater
“hard mother”, outermost layer, often fused with inner surface of skull. Thicker, protects CNS.
Characteristics of Arachnoid
“web form”, spiderweb appearance, thin, loose CT.
Subarachnoid space between arachnoid and pia mater traps CSF (circulates and is absorbed here).
Pia Mater
“soft mother”, innermost layer, adheres to surface of CNS
Where can CSF be found?
Ventricular system and subarachnoid space. Also in the central canal running through core of spinal cord.
Where is CSF formed?
Most is formed at the Choroid Plexus in the lateral third and fourth ventricles.
Where is CSF absorbed?
Subarachnoid space, into venous sinuses through arachnoid villi.
Absorption is unidirectional - can flow from SAS to venous outflow, but not the other way.
What are the functions of the CSF?
Protect brain and spinal cord
Waste control system
Distribution of some peptide hormones and growth factors
Maintain consistent extracellular microenvironment for neurons and glia (micronutrients).
What is the cause of the low permeability of the BBB?
Endothelial cells forming capillary walls are tightly fused (tight junctions) rather than having pores between them.
Foot processes of astrocytes around entire outer surface of capillary.
How are important nutrients transported across the BBB?
facilitated transport with carrier molecules
receptor mediated transcytosis
adsorptive transcytosis
BBB is highly permeable to
H2O, CO2, O2, most lipid soluble substances
BBB is slightly permeable to
electrolytes (Na, Cl, K)
BBB is impermeable to
Plasma proteins, non-lipid-soluble large organic molecules
Glucose transport across BBB
GLUT-1 facilitated diffusion
Large neutral amino acid transport across BBB
facilitated diffusion (Leu, Tyr, Val, phenylalanine)
How do small, neutral amino acids get through BBB?
They are synthesized in the CNS (Gly, Ala. Ser, Cys)
