Nervous System Flashcards
central nervous system
ONLY brain and spinal cord
peripheral nervous system
- everything else
– Sensory (afferent) neurons
– Efferent neurons: somatic motor and autonomic divisions
▪ Autonomic divided into sympathetic and parasympathetic branches
– Afferent neurons: sensory neurons
▪ Pain and senses - touching hot stove = afferent and taking it off = efferent
enteric nervous system
- only within the digestive system
- its own thing that can fxn on its own
– Network of neurons in the walls of the digestive tract
– Controlled by autonomic nervous system but is able to function autonomously
neurons carry what?
- electrical signals
- fxnal unit of the nervous system
neuron classification
– Structure – number of processes
▪ Multipolar (most common. neurons can go to so many other neurons), pseudounipolar, bipolar, anaxonic neurons
– Function
▪ Sensory (afferent) neurons, efferent neurons, and interneurons
- interneurons: inhibit action of another neuron
neuron structure
- cell body: integrating system. control center
- dendrites: receive incoming signals
- dendritic spines
- axons: carry outgoing signals
- axon hillock
anterior
ventral
posterior
dorsal
superior
postral, cephalic
inferior
caudal
what are nerves?
- axons bundled with connective tissue
– Sensory nerves, motor nerves, mixed nerves
ganglia and nucleus
- ganglia: cell body in PNS
- nucleus: CNS
- Ex: dorsal root ganglia=PNS
- something nucleus=CNS
fast axonal transport
- most organelles use this
– Moves organelles at rates of up to 400 mm/day
– Anterograde transport: from cell body to axon terminal (pos way)
– Retrograde transport: from axon terminal to cell body (neg way)
slow axonal transport
- think pain = v slow
– Moves material by axoplasmic (cytoplasmic) flow at 0.2–2.5 mm/day
schwann cells (PNS) and oligodendrocytes (CNS)
– Wrap around axon and form insulating myelin sheaths
▪ Nodes of Ranvier are gaps in insulation
- myelin sheaths: force action potential or message to go quicker
- oligodendrocytes: can connect to multiple neurones
satellite cells (PNS) - nonmyelinating schwann cells
– Ganglion outside of CNS (PNS) vs. nucleus inside CNS
plasticity
- reworking brain networks in response to day to day activities
affective behaviors
related to feeling and emotion
cognitive behaviors
related to thinking
the CNS is divided into what?
gray and white matter
gray matter
– Unmyelinated nerve cell bodies
– Clusters of cell bodies in the CNS are nuclei
– Dendrites
– Axon terminals
- cell body
white matter
– Myelinated axons
– Axon bundles connecting CNS regions are tracts
▪ Contain very few cell bodies
cerebrospinal fluid (CSF)
- brain just floats in this
- clear, no odor, no taste, cushion for the brain
- looks like water
- salty solution similar to plasma
- Produced by the choroid plexus in the ventricles
– Materials selectively moved from plasma to ventricles
– Water follows due to osmotic gradient - Surrounds entire brain
– Contained within subarachnoid space (between arachnoid membrane and pia mater)
– Flows from ventricles to subarachnoid space to return to plasma by villi - Function in physical and chemical protection
blood brain barrier
- highly regulated processes from astrocytes
- Highly selective permeability of brain capillaries
- Astrocytes foot processes promote tight junctions between endothelial cells
- Protects brain from toxic water soluble compounds and pathogens
- Small lipid-soluble molecules cross the blood-brain barrier
what do neurons need a constant supply of?
- oxygen and glucose
The brain receives how much blood pumped by the heart?
- 15%
oxygen
- passes freely across BBB
glucose
– Membrane transporters move glucose from plasma into the brain interstitial fluid
– Brain responsible for about half of body’s glucose consumption
– Progressive hypoglycemia leads to confusion, unconsciousness, and death.
spinal cord
- Segments associated with spinal nerves
– Spinal nerve branches into two roots
– Dorsal root neurons carry sensory information
▪ Dorsal root ganglia contain afferent (sensory) nuclei (sensation in the posterior side)
▪ Afferent neurons connect with interneurons in the dorsal horns
– Ventral roots carry motor information from the CNS to muscles and glands.
spinal cord gray matter
– Dorsal horns contain visceral & somatic sensory nuclei.
– Lateral horns contain visceral motor nuclei.
– Ventral horns contain somatic motor nuclei.
spinal cord white matter
– Divided into columns of tracts
– Ascending tracts take sensory information to the brain
– Descending tracts carry motor signals from the brain.
– Propriospinal tracts stay in the cord
spinal reflexes
- in a spinal reflex, sensory info entering the spinal cord is acted on w/o input from the brain
- sensory info about the stimulus may be sent to the brain
brain
- The brain stem is the oldest part of the brain
- 11 of 12 cranial nerves originate from the brain stem
- Cranial nerves can include sensory fibers, efferent fibers, or both (mixed nerves).
– Example: vagus nerve (cranial nerve X) is a mixed nerve
– Many nuclei are associated with reticular formation
▪ Controls wakefulness, sleep, muscle tone, pain modulation
precentral gyrus
- 95% motor
postcentral gyrus
- 95% sensation
medial, dorsal, and ventral movements
- medial = lower extremities
- dorsal = upper extremities
- ventral = face movement
vagus
- sensory and efferents to many internal organs, muscles, and glands
- most powerful parasymp neuron
- originates in CNS but part of PNS
brain stem
- medulla
- pons
- midbrain
medulla
– Medulla oblongata: regulatory system for heart rate, breathing, BP
– Somatosensory tracts vs. corticospinal tracts
– Pyramids
– Controls involuntary functions: blood pressure, breathing, swallowing, vomiting
pons
– Relay station, coordinates control of breathing
midbrain
– Eye movement, relay signals for hearing and seeing reflexes
cerebellum
- coordination of body movement
- second largest structure
- little brain
- Process sensory information and coordinate the execution of movement
– Equilibrium and balance (sensory) from somatic receptors
– Motor input from cerebrum
basal ganglia and cerebellum
- BG = what muscles need to contract
- cerebellum = how it should contract
thalamus
- relay station integrating center
hypothalamus
- releasing or inhibiting
- only affects ant pit gland
– Control of homeostasis
– Center for behavioral drives: for example, hunger, thirst
– Influences autonomic function and endocrine function
endocrine structures
– Pituitary gland
▪ Anterior
▪ Poster
– Pineal gland
the cerebrum is the site if higher brain fxns
- left side controls right side
- right side controls the left side
- Consists of two hemispheres connected by corpus callosum
- Gray matter and white matter
gray matter cerebrum
– Cerebral cortex –> inhibits movement
– Basal ganglia: control of movement (in CNS)
– Limbic system: link between cognitive functions and emotions
▪ Amygdala and cingulate gyrus: emotion and memory (fear and anger)
▪ Hippocampus: learning and memory
white matter cerebrum
– Found mostly on the interior
– Bundles of fibers connecting the different regions of the brain
brain fxn
1) Sensory system
– Monitors internal and external environments
– Initiates reflex response
2) Cognitive system
– Initiates voluntary responses
3) Behavioral state system
–Governs sleep-wake cycles and other intrinsic behaviors
cerebral cortex is organized into fxnal areas
- From a functional viewpoint, it can be divided into three specializations
1) Sensory areas
▪ Sensory input translated into perception (awareness)
2) Motor areas
▪ Direct skeletal muscle movement
3) Association areas
▪ Integrate information from sensory and motor areas
▪ Can direct voluntary behaviors - Cerebral lateralization
primary somatic sensory cortex
– Termination point of pathways from skin, musculoskeletal system, and viscera
– Somatosensory pathways
▪ Touch, temperature, pain, itch, body position
– Special Senses
▪ Visual cortex, auditory cortex, olfactory cortex, gustatory cortex
Sensory information is processed into perception
– Neural pathways extend from sensory areas to association areas, which integrate stimuli into perception
somatic senses
- Touch, proprioception, temperature, nociception (pain and itch)
- Pathways for somatic perception project to the cortex and cerebellum
- Receptors for somatic senses are located in skin and viscera
- Primary sensory neurons
– Synapse in CNS with secondary sensory neurons - Secondary sensory neurons
– Interneurons in the CNS - synapse with tertiary sensory neurons in thalamus - Tertiary sensory neurons
– Project to Somatosensory cortex and many project to cerebellum Somatosensory cortex
what is the most common receptor in the body?
- touch receptors
touch receptors are stimulated by different types of physical contact
– Stretch
– Steady Pressure
– Fluttering or stroking movements
– Vibrations
– Texture
* Found in the skin or deeper regions
* Examples
– Pacinian corpuscles
– Merkel receptors
skin temperature receptors are free nerve endings
- Terminate in subcutaneous layers
- Cold receptors
– Lower than body temperature - Warm receptors
– Above body temperature to about 45°C
– Pain receptors activated above 45°C - Thermoreceptors use cation channels called transient receptor potential (TRP) channels
nociceptors
– Neurons with free nerve endings
– Respond to strong noxious stimulus that may damage
tissue
– Found in the skin, joints, muscles, bones, and viscera
– Not found in CNS
activation is a reflexive protective response
– Integrated in spinal cord
– Two types of primary sensory fibers
▪ alpha delta fibers
- C fibers
alpha beta fiber
- large myelinated
- speed of conduction: 30-70 m/sec
- associated with mechanical stimuli
alpha delta
- small myelinated
- speed of conduction: 12-30 m/sec
- associated with: cold, fast pain, mechanical stimuli
c fibers
- small unmyelinated
- speed of conduction: 0.5-2 m/sec
- associated with: slow pain, heat, cold, mechanical stimuli
pain is a subjective perception
– Fast pain
▪ Sharp and localized—by alpha delta fibers
– Slow pain
▪ Duller and more diffuse—by C fibers
itch
– From skin nociceptors
– Histamine (and other substances) activate C fibers,
causing itch
gate control theory
- Aβ fibers synapse on inhibitory interneurons and increase inhibition
– Integrated response from Aβ and C fibers decreases the perception of pain.
analgesic drugs
– Aspirin – inhibits prostaglandins, decreases inflammation, and slows transmission of pain to site of injury
– Opioids
▪ Exogenous opioids bind opioid receptors
▪ Endogenous opioids include endorphins (b-endorphin), enkephalins, dynorphins
three major types
– Skeletal muscle movement
▪ Somatic motor division
– Neuroendocrine signals
▪ Hypothalamus and adrenal medulla
– Visceral responses
▪ Autonomic division
voluntary movement
– Primary motor cortex
– Motor association areas
Neuroendocrine and visceral responses are coordinated in the what?
- hypothalamus and medulla
the autonomic division
- Two subdivisions
– Sympathetic branch (“fight-or-flight”)
– Parasympathetic branch (“rest-and-digest”)
– Anatomically distinguishable
– Best distinguished by their relative activity under certain
situations
preganglionic neuron
– First neuron in chain with cell body located in CNS
– Projects from CNS to an autonomic ganglion outside the CNS
– Synapses with postganglionic neuron
postganglionic neuron
– Second neuron in chain with cell body located in the autonomic ganglion
– Projects from an autonomic ganglion to the target tissue
– Synapses with target cell
ganglion
– a cluster of neuronal cell bodies outside the CNS
– Also contain neurons completely within
– Act as mini-integration centers
autonomic pathways consist of how many neurons that synapse in an autonomic ganglion?
- two neurons
The Autonomic Nervous System Uses a Variety of Chemical Signals
- Both sympathetic and parasympathetic preganglionic neurons release acetylcholine (ACh) onto nicotinic cholinergic receptors (nAChR) on the
postganglionic cell - Most postganglionic sympathetic neurons secrete norepinephrine (NE) onto adrenergic receptors on the target cell
- Most postganglionic parasympathetic neurons secrete ACh onto muscarinic cholinergic receptors (mAChR) on the target cell
exceptions of the chemical signals
– Sympathetic cholinergic neurons (postganglionic) on sweat glands secrete ACh
– Nonadrenergic, noncholinergic neurons use other types of neurotransmitters
the adrenal medulla secretes catecholamines
- Neuroendocrine tissue
- Modified sympathetic ganglion
– Innervated by sympathetic preganglionic fibers
– Post-ganglionic neurons (chromaffin cells) lack axons
▪ Secrete epinephrine (neurohormone) into the blood
The Behavioral State System Modulates Motor Output
- Modulator of sensory and cognitive processes
- Neurons collectively known as diffuse modulatory systems
– Originate in reticular formation in brain stem
– Project axons to large areas of the brain - Reticular activating system controls consciousness
- Electroencephalography measures brain activity
sleep: four stages with two major phases
– Stages N1 and N2
– Slow-wave sleep (stage N3)
▪ Adjusts body without conscious commands
– Rapid eye movement (REM) sleep –> deep sleep
▪ Brain activity inhibits motor neurons to skeletal muscle, paralyzing them
▪ Dreaming takes place
sleep disorders
– Insomnia: inability to sleep
– Sleep apnea: stopping normal breathing during sleep
– Somnambulism: sleepwalking
Physiological Functions Exhibit Circadian Rhythms
- Circadian rhythm – alternating daily patterns of rest and activity
- bodies internal clock
- Primary “clock”
– Suprachiasmatic nucleus (SCN) of the hypothalamus
– Melatonin linked to circadian rhythms - Disruptions affect mental and physical health
– Shift work
– Jet lag
Emotion and Motivation Involve Complex Neural Pathways
- The limbic system is the center of emotion in the human brain
- Motivation is defined as internal signals that shape voluntary behaviors
- Some states known as drives
- Work with autonomic and endocrine responses
- Motivated behaviors stop when a person has reached a certain level of satiety
- Pleasure and addictive behaviors: link to dopamine
moods are similar to emotions
– Longer-lasting
– Related to one’s sense of well being
mood disorders
– Fourth leading cause of illness worldwide today
– Depression
▪ Sleep and appetite disturbances
▪ Alterations of mood and libido
▪ May affect function at school or work or in personal
relationships
▪ Antidepressant drugs alter synaptic transmission
integration of spoken language involves two regions
– Wernicke’s area – understanding language
– Broca’s area – produces speech
What is part of the endocrine system and secretes epinephrine and norepinephrine?
Postganglionic neurone
sympathetic
short preganglionic and long postganglionic
parasympathetic
long preganglionic and short postganglionic
where does majority of parasympathetic take place
- vagus nerve and sacral plexus
what neurotransmitter does the preganglionic secrete in the para and symp?
para and sym secrete acetylcholine
what neurotransmitter does the postganglionic secrete in the para and symp?
para secretes acetylcholine and symp secretes epinephrine
where does sympathetic take place?
T1-L2
