Final! Flashcards
Synaptic relationships between neurons
- Communication of one neuron with another at a synapse
- Also communication with another cell- neuromuscular junction
- One spinal motor neuron can have 10,000 synaptic knobs from other neurons on it
- one cerebellum neuron can have as many as 100,000
Synapses
- can be many synapses on a some- if enough of them “fire” on a soma a local potential
- two types of synapses
- • chemical and electrical
Acetylcholine
- Found in the neuromuscular junctions, most synapses of autonomic nervous system, retina, and many parts of the brain
- Excites skeletal muscles, inhibits cardiac muscle, and has excitatory or inhibitory effects on smooth muscle and glads depending on location
Glutamate (glutamic acid)
Found in cerebral cortex and brainstem;retina
Accounts for about 75% of all excitatory synaptic transmission in the brain; involved in learning and memory
Aspartate (aspartic acid)
Found in spinal cord
Effects similar to those of glutamate
Glycine
Found in inhibitory neurons of the brain, spinal cord, and retina
Most common inhibitory neurotransmitter in spinal cord
GABA
- Found in thalamus, hypothalamus, cerebellum, occipital lobes of cerebrum, and retina
- most common inhibitory neurotransmitter in the brains
Norepinephrine
- Found in sympathetic nervous system, cerebral cortex, hypothalamus, brainstem, cerebellum, and spinal cord
- involved in dreaming, waking, and mood
- excites cardiac muscle
- can excite or inhibit smooth muscle and glands depending on location
Epinephrine
- found in hypothalamus, thalamus, spinal cord, and adrenal medulla
- effects similar to those of norepinephrine
Dopamine
- found in hypothalamus, limbic system, cerebral cortex, and retina
- highly concentrated in substantia nigra of midbrain
- involved in elevation of mood and control of skeletal muscles
Serotonin
- found in hypothalamus, limbic system, cerebellum, retina, and spinal cord
- also secreted by blood platelets and intestinal cells
- involved in sleepiness, alertness, thermoregulation, and mood
Histamine
- found in hypothalamus
- also a potent vasodilator released by mast cells of connective tissue and basophils of the blood
Substance P
Found in basal nuclei, midbrain, hypothalamus, cerebral cortex, small intestines, and pain-receptor neurons
Mediates pain transmission
Enkephalins
- found in hypothalamus, limbic system, pituitary, pain pathways of spinal cord, and nerve endings of digestive tract
- acts as analgesics (pain-relieved) by inhibiting substance P
- inhibit intestinal mortals
- secretion increases sharply in women in labor
Beta endorphins
- found in digestive tract, spinal cord, and many parts of the brain
- also secreted as a hormone by the pituitary
- suppresses pain
- reduces perception of fatigue and many produce “runner’s high” in athletes
Cholecystokinin
Found in cerebral cortex and small intestines
Suppresses appetite
An exciting cholinergic synapse
Cholinergic
Postsynaptic potential
An inhibitory GABA-ergic synapse
GABA
Works the same as stimulators cholinergic synapses
But- this GABA receptor is a Cl- channel
-inhibits the neuron
An andrenergic Synapse
Enzyme amplification
Source of norepinephrine can be in the synapse or bloodstream
Cessation of the signal
Diffusion- neurotransmitter diffuses away, astrocytes pick it up and return it to the neurons
Reuptake- synaptic knob reabsorbs neurotransmitter and break them down with monoamine oxidase, MAOI (monoamine oxidase inhibitors are powerful antidepressants)
Degradation in the synaptic cleft- acetylcholinesterase (for example),reabsorbed by synaptic knob
Neural integration
This is where “though@, memory and all the good stuff related to processing come in to play
Most neurons have many input axons articulating with it
This network of nerves and synapses is what we are going to talk about
Postsynaptic potentials
Can be exciting or inhibitory
Increase/decrease the rate at which a neuron fires because neurons all depolarize are a certain background rate
Summation, facilitation and inhibition
EPSPs and IPSPs reach a postsynaptic neuron and depending on the balance the neuron fires-this is how we process
Summation- adding up PSPs giving a net effect in the trigger zone
- temporal summation- EPSPs are generated at a high rate, there is no time for the signal to decay between signals
- spatial summation- EPSPs from several synapses add up to the threshold at the hillock
Facilitation and presynaptic inhibition
Facilitation- where more than one neuron cooperates to stimulate the postsynaptic neuron
Presynaptic inhibition- when on neuron inhibits and counteracts the effects of other neurons
Memory and synaptic plasticity
Memory is not individual cells it is a pathways called a memory trace (engram)
- pre-existing pathways are modified in response to experience (synaptic plasticity)
- takes 1-2 hours
- when you learn something you form and reform a pathway until it gets easier and more efficient- called synaptic potentiation
Immediate, short, and long-term memory
Immediate memory
You need to be able to hold on to some thoughts to be able to function
- example reading- you have to remember the earlier words in the sentence to function
Seems to be based on reverberating circuits
-keeps it active long enough to use it later
Short-term memory
Lasts for a few second to a few hours
Easy to forget things in STM
- probably carried out mainly by reverberating circuits
- longer-lasting memories seem to be made by making a neuron hyper-sensitive by stimulating it over and over- it fires more easily and stronger
-• you try hard to program something in, and it is “jogged” very easily and comes back strong
Long-term memory
Declarative - having to do with language Procedural - retention of motor skills Physical remodeling of synapses Experienced synapses get easier and easier to remodel and better and better at what they remember the more you use the information
The spinal cord functions
Conduction - sensory info to the brain - motor commands reach the effectors Routing of input around the cord Locomotion - simple repetitive muscle contractions, like in walking, are controlled from the spinal cord -• central pattern generators Reflexes - involuntary responses to certain stimuli that are always the same
Anatomy
Cord and 31 ours of spinal nerves
C, T, L, and S regions
Cervical enlargement- where nerves of upper limbs originate
Lumbar enlargement- where nerves of the pelvic region and lower limbs originate
Medullary cone-> cauda equina
Spinal cord meninges
Meninges- three fibrous membrane layers that cover brain and spinal cord
Separation and protection
Spina bifida
When one or more vertebrae fail to form a complete vertebral arch
Meninges and even parts of the spinal cord can exist outside of the spinal canal
This is why women should take folic acid during the earliest part of pregnancy
Cross-sectional anatomy
Gray matter- proximal parts of axons and neurons- little myelin - dorsal horns -ventral horns - gray commissure -central canal - lateral horn White matter- bundles of axon (tracts)- lots of myelin - columns, funiculi -tracts, fasciculi
Spinal tracts
White matter- bundles of axons
Ascending and descending
Each had different functions
Important for understanding spinal cord injuries
Poliomyelitis and amyotrophic lateral sclerosis
Motor neurons
Polio- nerves of the brainstem and central horn of the spinal cord
- anything from paralysis to cessation of breathing (a brainstem function)
ALS= Lou Gehrig disease- degeneration of motor neurons and sclerosis of lateral portions of the spinal cord
- astrocytes fail to reabsorb glutamate (it becomes toxic)
-sensory and intellectual functions remain
Afferent fibers
Carry sensory signals from receptors to the CNS
Efferent fibers
Carry motor signals from the CNS to effectors
Somatic fibers
Inner age skin, skeletal muscles, bones, and joints
Visceral fibers
Inner are widespread organs such as muscles, skin, glands, viscera, and blood vessels
Special fibers
Inner are more localized organs in the head, including the eyes, ears, olfactory and taste receptors, and muscles of chewing, swallowing, and facial expression
Branches and entry points for spinal nerves
Divides into rootless where it enters
Dreamtime map
This one is good to know- and fairly logical
Dermatome- a specific region of the skin that sends nerves to a specific spinal nerve
Disorder- shingles
- chickenpox virus remains in the dorsal root ganglion for life after an infection
- it is usually kept under control by the immune system
- during immune compromise (stress is a common cause) the virus can move down the axons via fast axons transport
- causes inflammation, pain (postherpetic neuralgia, PHN), discoloration, and formation of vesicles
- the pain can linger for months or years after an outbreak
- treatment- anti-inflammatory Ed, antidepressants
Somatic reflexes
- quick, involuntary, reactions that are always the same
- require stimulation- not spontaneous- response to sensory input
- are quick- usually don’t use very many inter neurons
- involuntary-direct reaction to stimulation, you can’t control it, stop it, awareness is not part of the reflex- you can be asleep, doesn’t require an intact spinal cord
- stereotyped- they are the same every time
Pathway of a somatic reflex arc
Somatic receptors Afferent nerve fibers Integrating center- one or more interneurons Efferent nerve fiber Skeletal muscles
Four types of reflexes
Stretch reflex Flexor reflex Crossed (withdrawal) reflex Cross extension reflex Golgi tendon reflex
Stretch reflex
- maintains equilibrium and posture
- when muscles are stretched- they fight back by contracting (example- head going forward)
- tendon reflex (stronger version of this)
- very fast- monosynaptic
- reciprocal inhibition- so that the muscles do not fight each other
Flexor reflex
Involves complex pathways in order to contract and relax appropriate muscles at the same time
Crossed extension reflex
Helps maintain balance and postur when another reflex is activated (like flexor reflex)
Contralateral, ipsilateral, or intersegmental reflex arcs (other side of body)
Golgi tendon reflex
Located in the tendon- detects over stretching by compression of a nerve ending in tendon
Inhibits alpha motor neurons from giving continues contraction signals
Also makes muscle contraction mor evenly spread throughout a muscle
The meninges
- connective tissue membranes
- only the meningeal layer is continuous with the spinal meninges
- sinuses- T in the back of head drains to jugular
Meningitis
- inflammation of the meninges
- viral or bacteria- invades via nose and throat
- usually pia matter and arachnoid matter then to nervous tissue
- can cause swelling of the brain and brainstem hemorrhage
- can be diagnosed by looking at the cerebral spinal fluid- lumbar puncture- subarachnoid space
- • the spinal cord does not extend all the way down there so it is a relatively safe procedure
Functions of the CSF
Buoyancy
- similar density to the brain- the brain is suspended in the CSF
- even support all around the brain so it does not crush itself under its own weight
Protection
- from trauma (blows to the head)
- very hard blows can still cause the brain to suffer shearing damage because it can hit the cranial floor
Chemical stability
- rinses wastes and regulates the brain chemical environment
The CSF flows
- pulsation of the brain and the cilia of the ependymal cells drive the fluid
- flows in a circuit and is absorbed
Hydrocephalus
- accumulation of CSF usually from a blockage
- • interventricular foramen, cerebral aqueduct, apertures of the 4th ventricle
- •expands and pushes against the brain tissue and cause damage
- • treated by inserting a shunt
Blood supply and blood brain barrier
- the brain uses a disproportionately large amount of the blood supply
- • 10 seconds interruption causes unconsciousness
- brain barrier system- regulates when enters the brain
- • blood capillaries
- • capillaries of the choroid plexus
- • tight junctions between ependymal cells in blood-CSF barrier
- • tight junctions between capillary endothelia in blood-brain barrier (BBB)
- • protection
- • also protects us from pharmaceuticals that we want to have there- a challenge for drug designers
- • the barrier is absent at the cricumventricular organs (CVOs) in the 3rd and 4th ventricles- a common route to infection
- •- these organs need to have access to blood for assessing blood glucose, pH, etc.
Hindbrain and midbrain- medulla oblongata
- myencephalon becomes the medulla oblongata
- • ridges or pyramids on anterior surface
- • olive and inferior olivary nucleus receive info from brain and relay it to cerebellum
- • contains
- •- cardiac center
- •- vasomotor center
- •- respiratory centers
- •- coughing, sneezing, salivation, swallowing, gagging, vomiting, gastrointestinal secretion, sweating, speech, tongue and head movements
Hindbrain and midbrain- the pons
- develops from the metencephalon
- contains nuclei that relay signals from the cerebrum to the cerebellum
- sleep, hearing, facial sensation, respiration, swallowing, bladder control posture
The hindbrain- cerebellum
- hemispheres separated by vermis with folia
- connected to brainstem by cerebella pundicles
- coordinates movements, core donates with inner ear (equilibrium), proprioception, some relexes
- recent discoveries- evaluation of some sensory input (movement, some senses, language, emotion, eye movement, timekeeping, pitch, impulse control, ADHD)
The midbrain
- connects the hindbrain and the forebrain
- contains the cerebral aqueduct
- control of awareness to pain, various functions in controlling vision and eye movement
The reticular formation
- runs through all levels brainstem and projects to many areas of the cerebrum
- some of the functions of its networks
- • somatic motor control
- • cardiovascular control
- • pain modulation
- • sleep and consciousness
- • habituation- ignoring repetitive stimuli
The forebrain- the diencephalon
Thalamus
- gateway the cerebral cortex
- taste, smell, hearing, equilibrium, vision, and some of the somesthetic senses
- relays motor control signals
- memory and emotion of the limbic system
Hypothalamus
- major control center of the autonomic nervous system and endocrine system
- huge number of functions we will see in other chapters
Epithalamus
- pineal gland and havenula
The forebrain- cerebrum
- has many gyri- allows for more surface area and more white matter
- the integration center- tracts and cortex
- • many higher functions we associate with judgment, thinking, emotions, complex senses, complex language
- frontal lobe
- parietal lobe
- occipital love
- temporal lobe
- insula
Tracts of the cerebral white matter
- projection tracts- connect higher and lower brain
- commissural tracts- connect one hermit to another
- association different regions of the same hemisphere
- • “enable you to smell a rose, name it, and picture what it looks like”
The cerebral cortex
- gray matter
- neocortex- most developed in the primates (recent, see figure)
- the integrating center of the surface of the cerebrum
The limbic system
- centers of emotion and learning, memory
- gratification and aversion centers
Higher forebrain functions
- this is an overwhelming amount of material
- examples:
- •electroencephalogram
- •sleep
- •diagram of functional regions (different association areas)
- •lateralization
Electroencephalogram
- there are rhythmic voltage changes in the superficial cerebral cortex
- can be recorded on the scalp
- are used to diagnose brain function
- •alpha waves- when the mind is awake but resting
- •beta waves- mental activity and sensory stimulation
- •theta waves- children, adults that are drowsy or sleeping
- •delta waves- infants, adults deep sleep
The autonomic nervous system and visceral reflexes
- general properties of the autonomic nervous system
- •visceral reflexes
- •divisions
- •neural pathways
- anatomy of the autonomic nervous system
- •sympathetic and parasympathetic divisions
- •adrenal glands
- autonomic effects on target organs
The autonomic nervous system
- regulates very primitive functions like blood pressure, heart rate, and body temp
- unconscious processes- involuntary
- has numerous implications for treatment of patients
- Mai dance of homeostasis
- autonomic nervous system- motor nervous system that controls glands, cardiac muscle, and smooth muscle
What is autonomic?- biofeedback example
- Hypertension, stress, and migraine headaches have been treated using this technique
- these problems are normally thought of as malfunctions in the autonomic systems
- a patient can learn to control them by getting constant feedback on their status (via lights or auditory signals) and thinking about them
Visceral reflexes involve an arc
Example: high blood pressure that is being reduced
- receptors
- afferent neurons
- interneurons
- efferent neurons
- effectors
The autonomic nervous system- divisions
- sympathetic division
- parasympathetic division
- they work in the background all the time and are both on all the time
- •autonomic tone-background rate of activity
- •examples: parasympathetic tone down-regulates the heart rate to 70-80 bpm; sympathetic tone keeps the blood vessels contracted so that you have blood pressure
Sympathetic division
Adapts the body to for physical activity (increases alertness, heart rate, blood pressure, pulmonary airflow, blood glucose, and blood flow to muscle; decreases blood flow to the skin and digestive tract)
- in the extreme- the “fight or flight response@
Parasympathetic division
Has a calming effect on the body, reduced energy expenditure (functions like digestion and waste elimination)
-“resting and digesting” state
Connects to organs
Remove that the vagus connects to almost everything
Preganglionic fiber- always cholinergic
Postganglionic fiber- always cholinergic
Sympathetic pathways
-only memorize what they connect to
-short preganglionic and long postganglionic fibers
-sympathetic chain of ganglia
Preganglionic fiber- always cholinergic
Postganglionic fiber- mostly adrenergic; a few cholinergic
Three different sympathetic pathways
Lateral horn
Spinal nerve route
Sympathetic nerve route
Splanchnic nerve route
Adrenal glands
- adrenal cortex- secreted steroid hormones
- adrenal medulla- like a sympathetic ganglion secreted epinephrine, norepinephrine, dopamine
Understanding the up-regulating and down regulating roles
- why is it that epinephrine can stimulate the heart to contract faster, relax the smooth muscles in the lungs to dilate the bronchi, and cause the blood vessels in the body to contract (except those in the heart- they dilate)????
- depends on the neurotransmitters secreted by the fibers
- •cholinergic fibers- secrete acetylcholine
- •adrenergic fivers- secrete norepinephrine
- depends on the receptors the target has
- •cholinergic receptors
- •adrenergic receptors
Cholinergic receptors
Acetylcholine binding
- nicotinic receptors (curare binds here too)
- •postsynaptic cells all ganglia, adrenal medulla, neuromuscular junctions
- muscarinic receptors (atropine binds here too)
- •occur on all gland, smooth muscle, cardiac muscle that receive cholinergic enervation
Adrenergic receptors
Alpha adrenergic receptors
-usually excitory
-in most blood vessels, causes vasoconstriction
Beta adrenergic receptors
-usually inhibitory
-in blood vessels to the heart and skeletal muscles, causes vasodilation, in bronchioles
-•relaxes airway
Dual innervation
- sympathetic and parasympathetic
- used to up or down regulate an organ
- without both it is trickier to control
- can be antagonistic or cooperative
Dual innervation- cooperative effects
- Examples: salivation- the sympathetic and parasympathetic are both stimulators, but on two different cells in the glands
- (glands are often stimulated by increasing blood flow-and therefore filtration)
Control without dual innervation
- example: vasomotor tone
- have a baseline sympathetic tone
- stronger or weaker tone from sympathetic fiber
- frequency of firing
Horner syndrome
Chronic unilateral pupillary construction, sagging of the eyelid, withdrawal of the eye into the orbit, flushing of the skin, and lack of facial perspiration, resulting from lesions in the cervical ganglia, upper thoracic spinal cord, or brainstem that interrupt sympathetic innervation of the head
Raynaud disease
Intermittent attacks of paleness, cyanosis, and pain in the fingers and toes, caused when cold or emotional areas triggers excessive vasoconstriction in the digits; most common in young women. In extreme cases, causes gangrene and may require amputation. Sometimes treated by severing sympathetic nerves to the affected regions
Cranial nerve I
Olfactory
Function: smell
Sensory
Cranial nerve II
Optic
Function: transmits retina input
Sensory
Cranial never III
Oculomotor
Function: constricts pupils, innervates extraocular muscles, moves upper eyelid, moves eye up, down and medially
Motor
Cranial nerve IV
Trochlear
Function: eye movement towards nose
Motor
Cranial nerve V
Trigeminal
Function: sensation to face
Both
Cranial nerve VI
Abducens
Function: eye movement laterally
Motor
Cranial nerve VII
Facial
Function: facial muscles(smile, frown, whistle, raise eyeballs, close eye, and other facial actions)
Both
Cranial nerve VIII
Vestibulocochlear
Function: hearing and equilibrium
Sensory
Cranial nerve IX
Glossophryngeal
Function: sensation from tongue, throat, and outer ear. Controls food intake, and even some cardiovascular and respiratory
Both
Cranial nerve X
Vagus
Functions: supply organs head, neck, thoracic, and abdominopelvic. Cardiac, pulmonary, digestive, and urinary functions
Both
Cranial nerve XI
Accessory
Function: speaking
Motor
Cranial nerve XII
Hypoglossal
Functions: tongue movements of speaking, eating, and swallowing
Motor
