Central Nervous System Flashcards
Cannons Postulates (4)
- Nervous regulation of internal environment
- Tonic control
- Antagonistic control
- One chemical signal can have different effects in different tissues
CNS
Brain and spinal cord
PNS
All nerves connecting to the CNS, cranial and spinal nerves
Gray matter
Unmyelinated nerve cells
White matter
Myelinated axons, few cell bodies
Cranium
Bony skull that encases the brain
Vertebral column
Bone where spinal cord runs through
Meninges
Membrane between bone and tissues
Types of meninges
Dura mater, arachnoid membrane, pia mater
Purpose of meninges
Cushion and protect delicate neural tissue
Order the layers of the meninges from inside to outside
Pia mater (most inner) –> arachnoid mater –> dura mater (most external)
Spinal nerve roots
Dorsal and ventral
Dorsal spinal nerve root
Sensory
Ventral spinal nerve root
Motor
Dorsal root gray horn
Process sensory information
Ventral root gray horn
Send out motor information
Ascending vs. descending tracts
Ascending= carry signals to brain
Descending= carry signals from brain
Spinal reflex
Initiates a response without input from the brain (ex. pulling hand away from something hot)
Spinal cord serves as an….
Integrating center
SEQ process of reflexes
Sensory receptor produces a sensory potential in response to stimulus –> sensory neuron conducts action potentials –> processed by brain or spinal cord gray matter –> action potential from integrating center travels to motor neuron –> effector (reflex)
Blood-brain barrier
Protects the brain from harmful substances, HIGHLY selective permeability –> mediated by astrocyte foot processes and tight junctions
Astrocyte foot processes
Secrete paracrines that promote tight junction formation
Tight junctions
Prevent solute movement between endothelial cells –> keep blood-brain barrier highly selective
Cerebral spinal fluid
Clear and colorless, protects brain from chemical and physical injury, circulates through various openings in the brain and subarachnoid space
What produces the cerebrospinal fluid?
Choroid plexus
Choroid plexus
At the center of the brain, produces cerebrospinal fluid
Subarachnoid space
Provides a layer of cushioning for the brain
Metabolic requirements of the brain
Oxygen, glucose
Brain is responsible for what percentage of glucose consumption?
50%
What passes freely across blood-brain barrier?
Oxygen, brain requires high oxygen
What percentage of oxygenated blood pumped by heart does brain recieve?
15%
Frontal lobe
Primary motor cortex, motor association area, responsible for skeletal muscle movement
Parietal lobe
Primary somatosensory cortex, sensory association area
Occipital lobe
Visual association area, visual cortex
Temporal lobe
Auditory cortex, auditory association area
Olfactory cortex
Smell
Gustatory cortex
Taste
Brain association areas
Integrate information from sensory and motor areas, direct voluntary behaviors
Brain sensory areas
Sensory input translated into perception
Brain motor areas
Direct skeletal movement
Diencephalon
Inner brain: hypothalamus, thalamus, pineal gland, pituitaries (anterior, posterior) –> centers for homeostasis
Hypothalamus
Activates sympathetic nervous system, maintains body temperature, controls osmolarity, reproductive functions, food intake, influence behavior and emotions, influences cardiovascular control center, secretes trophic hormones that control release of hormones from AP
Motivation state
Internal signals that shape voluntary behaviors, states of drive, autonomic and endocrine responses
Behavioral state
Modulates sensory and cognitive processes, modulates motor output
Diffuse modulatory systems
Group of neurons that influence attention, motivation, wakefulness, memory, motor control, mood, metabolic homeostasis –> originate in the reticular formation
4 diffuse modulatory systems
Noradrenergic, serotonergic, dopaminergic, cholinergic
What system of the brain creates emotion?
Limbic system
Phineas Gage incident
Damage to frontal lobe, had change in personality, rational decision making
Symptoms of frontal lobe damage
Memory deficits, loss of spontaneous behavior, apathy, impaired attention, depression, elevated mood, impulsivity –> may have normal IQ
4 major steps of sensation
- stimulation of sensory receptor
- Transduction of stimulus
- Generation of action potentials
- Integration of sensory input
Types of sensory receptors
Encapsulated nerve endings, free nerve endings, separate cells (neurotransmitters required)
Receptive fields
Receive sensory input, attached to a sensory neuron or group of sensory neurons –> can be large or small, depending on location, can overlap
Properties of stimuli
Nature (modality, ie. touch, smell, hearing, etc.), location, intensity, duration
Overlapping receptive fields
One receptive field may generate more action potentials than another, depending on where the sensation occurs in the overlap
Two-point descrimintation
Size of receptive field determines whether or not points can be discriminated –> more, smaller fields= more ability to discriminate sensations
Visceral reflexes
Spinal cord reflex, usually do not reach conscious perception –> integrated in brainstem or spinal cord
Perceptual threshold
Level of stimulus necessary to be aware of particular sensation
Modality of stimulus
Where sensory neurons are activated, specific receptor types
Labeled line coding
1:1 association of a receptor with a sensation
Population coding
Multiple receptors working together to send more information to CNS than can be provided by one receptor
Lateral inhibition
Increases contrast between activated receptive fields and inactive neighbors –> determination of very fine stimulus
What is the one exception to location stimulus rule?
Auditory, ears are only sensitive to frequency, no receptive fields –> use this information to determine location (easier to percieve)
Intensity of stimulus
Number of receptors activated, frequency of action potentials
Duration
Coded by duration of action potentials, some receptors can adapt/cease to respond
Phasic receptors
Fast receptors
Tonic receptors
Slow receptors
Somatic senses
Touch, proprioception, temperature, nociception
Nociception
Pain, itch
Merkel receptors
Sense steady pressure and texture
Meissner’s corpsucle
Response to flutter and stroking movements
Ruffini corpuscle
Response to skin stretch
Pacinian corpuscle
Senses vibrations
Hair root sensation
Free nerve endings wrapped around follicles that sense hair movement
Temperature receptors
Free nerve endings, termination in subcutaneous layer
Warm temperature receptors
Active above body temperature, also activated with pain receptors –> painful heat (burning)
Cold receptors
Active below body temperature
Nociceptors
Respond to strong noxious stimului (chemical, mechanical, thermal) that may damage tissue, modulated by local chemicals (substance P)
Substance P
Secreted by primary sensory neurons when tissue is injured, stimulate pain –> cause of inflammatory pain
Two nociceptor pathways
Reflexive protective, ascending pathway to cerebral cortext
Reflexive protective pathway of nociception
Withdrawal reflex, integrated in spinal cord (ex. touching hot stove)
Ascending pathway to cerebral cortex pathway of nociception
Pain/itch becomes conscious sensation
Classes of somatosensory nerve fibers
Aβ, Aδ, C
Aβ nerve fibers
Large, myelinated –> mechanical stimuli
Aδ nerve fibers
Small, myelinated –> cold, fast pain, mechanical stimuli
C nerve fibers
Small, unmyelinated –> slow pain, heat, cold, mechanical stimuli, ITCH
Rank nerve fibers from slowest to fastest
C, Aδ, Aβ
Itch
C fibers activated by histamines
Pain
Subjective perception, fast and sharp (delta fibers), or slow and dull (C fibers)
Gate control theory of pain
Pain fibers are blocked by interneurons until a painful stimulus is detected –> interneuron block removed and integration center is signaled
Referred pain
Convergence of somatic and visceral first-order neurons on the same second-order neuron, interpretation by the brain as pain coming from somewhere else
Chemoreception
Smell and taste
Olfaction
Detection of scents by olfactory epithelium (cells in the nose), odorants bind to odorant receptors
Odorant receptors
G-protein-cAMP linked membrane receptors
Light receptor cells
Photoreceptors
Optic chasm
Where the optic nerves cross
Vestibular apparatus
Provides information about movements and position in space
