Week 7

Chapter 42

primary functions of the nervous system

→ receive information: environmental stimuli (external and internal)

→ translate (integrate) information: evaluate stimuli

→ send a response: initiate and send a response to the effector; coordinate rapid, immediate responses

→ location of nerve or nerve-like activity: all animals with tissues

→ exception: poriferans (sponges) → electrical regulation of porocytes

nerve nets in invertebrates

→ interconnected neurons, no central control point (ganglia or brain) for movement and response to stimuli

→ responses from multiple directions (good for detecting prey) and bidirectional

→ no separation of function (sensory, integration, motor)

→ clade radiata, phylum cnidaria and clade bilateria, phylum echinodermata

clade radiata, phylum cnidaria nerve nets

→ some jellyfish have two nets

→ slow-transmission net: coordinates tentacles

→ faster net: coordinates swimming

clade bilateria, phylum echinodermata nerve nets

→ modified nerve net (radial nervous system)

→ coordinates tube feet and arm movement

bilateral nervous systems

→ control point (ganglia or brain) and interconnected neurons for integration (stimulus intensity, direction, etc.) and coordination of movements and responses

→ the response is localized, unidirectional neurons, and separation of function (sensory, integration, motor)

→ phylum platyhelminthes, phylum annelida, phylum arthropoda, phylum cephalopoda

phylum platyhelminthes bilateral nervous system

→ the brain is necessary for full, coordinated, and adaptive responses

→ ganglion provides segmental (localized) control

→ nerve cord is solid and ventral

→ forward movement with some segments; elongating and other shorting at the same time

phylum arthropoda bilateral nervous system

→ insects have the largest brains in the phylum

→ workers have more neurons for learning, memory, olfactory processing

→ e.g., foraging ants count their steps → experiment: changing the length of ant’s legs

phylum cephalopoda

→ the brain is lobed and has intricate folds that are similar to vertebrates and regions are well-developed for specific functions (somewhat unique)

→ senses are well-developed

→ e.g., octopus

• greatest brain size per body size of all animals

• significant ability to learn, and perform difficult tasks (problem solve and use tools)

• changes color, skin, and shape

overall trends in the evolution of the nervous system

→ the number of nerve cells increased

→ nerve cells became concentrated in specific areas (not simply spread throughout the body; ganglia, brain, nerve cord, and nerves)

→ specialization of function and regions (no longer like nerve net)

→ cephalization: concentration of sensory organs on the anterior end of the body

central nervous system (CNS)

integrates information and sends an appropriate response

→ brain (cranium) and spinal cord (vertebral column; dorsal, hollow tube)

nerves

→ cranial (12 pairs) and spinal nerves (32 pairs)

→ CNS connects to PNS

→ afferent, integration, and efferent nerves involved

peripheral nervous system (PNS)

connects to but lies outside the brain and spinal cord and carries information to and from body parts and regions

→ afferent nerves, efferent nerves, and integration

afferent nerves

carry information to CNS from sensory receptors

efferent nerves

carry information back to effectors from the CNS (homeostasis)

integration

occurs in CNS (information processing leading to a response)

divisions of the PNS

somatic and autonomic

somatic division of the PNS

skeletal muscle and skin, voluntary muscle movement (conscious activities)

autonomic division of the PNS

involuntary responses, control internal organs (viscera)

→ e.g., heart rate, blood flow, respiratory rate

divisions of the autonomic division of the PNS

parasympathetic and sympathetic

parasympathetic division of the autonomic division of the PNS

maintain minimal energy level, resting and digesting activities, neurotransmitter: acetylcholine

sympathetic division of the autonomic division of the PNS

mobilize energy, decrease non-vital functions, stimulate the adrenal gland (release epinephrine), fight or flight

autonomic nervous system (ANS)

helps maintain homeostasis since sympathetic and parasympathetic divisions generally work in opposite ways

→ enteric system which is embedded in the digestive tract is also part of the ANS

ANS functions on the pupil

→ sympathetic: dilation

→ parasympathetic: constriction

ANS functions on the heart

→ sympathetic: increased rate contraction

→ parasympathetic: decreased rate contraction

ANS functions on the arteries

→ sympathetic: vasoconstriction

→ parasympathetic: vasodilation

ANS functions on the lungs

→ sympathetic: bronchial relaxation

→ parasympathetic: bronchial constriction

ANS functions on the kidneys

→ sympathetic: decreased urine production

→ parasympathetic: increased urine production

ANS functions on sweat glands

→ sympathetic: increased sweating

→ parasympathetic: no change

reflexes

→ protective function

→ PNS connects with CNS and is involved in cranial or spinal pathways

→ spinal reflex: withdrawal reflex

golgi tendon (muscle spindle) stretch reflex

→ spinal cord reflex

→ monosynaptic (true for stretch reflexes)

→ unisegmental

→ ipsilateral (all on one side)

→ reciprocal innervation (opposing muscle groups)

→ contraction opposite to the stretch initiator

withdrawal and cross-extensor reflex

→ excitatory and inhibitory interneuron, withdrawal on the stimulated side of the body, extension on the opposite side

→ intersegmental response: response on both sides of the cord

→ ipsilateral response: withdrawal (right leg), extensors inhibited, flexors stimulated

→ contralateral response: extension (left leg), flexors inhibited, extensors stimulated

→ the same thing occurs if someone grabs one of your arms unexpectedly

evolution of the vertebrate brain

→ brain and spinal cord differentiate from the neural tube

→ anterior neural tube region expands and the brain develops, differentiates into hindbrain, midbrain, and forebrain

→ posterior neural tube region develops into the spinal cord

cerebellum

→ located dorsal to the pons and medulla

→ ~1/2 of neurons

→ function: hand-eye coordination, smoothly coordinated movement, equilibrium, posture

medulla

→ part of both the hindbrain and brain stem, located just inside the foramen magnum and continuous transition with the spinal cord

→ life-sustaining functions

choroid plexus

specialized capillary bed located in the ventricles

→ epithelial cells form a blood-CSF barrier

→ produces much of the CSF (ultrafiltrate of plasma)

nerve tracts in medulla

→ connect the spinal cord and brain

→ decussation of the pyramids: crossing over the cortical spinal tracts

decussation

crossing over of nerve tracts in the CNS

pons

→ lies superior to the medulla and anterior to the cerebellum and is part of both the hindbrain and brainstem

→ connects (bridges) higher brain centers with cord, cerebrum with the cerebellum, two sides of the cerebellum

→ functions: with medulla, helps regulate respiration

midbrain

→ lies superior to the pons, inferior to the thalamus and is part of the brainstem

→ motor movement of eyes: coordinate eye and head movements to follow an object, turn head toward unexpected sound

→ auditory processing, muscle tone, and posture, pain modulation, mood regulation

forebrain

sits at the top of the brain stem and includes thalamic structures, the cerebral hemispheres, and the limbic system

→ thalamus, hypothalamus, and epithalamus

thalamus

has motor and sensory connections cord with the cerebral cortex

→ filtering and sorting (send to the appropriate region in the cerebrum)

→ crude sense of stimuli (not olfaction (CN I)

hypothalamus

lies below the thalamus that has visceral control (regulation of autonomic and somatic response)

epithalamus

regulates the sleep-wake cycle and emotions

→ pineal gland secretes melatonin

cerebrum

most superior part, ~83% of brain mass, and second largest surface area

→ consists of the cortex, inner portion, lobes, hemispheres, gyri, sulci, fissures, and corpus callosum

→ sensory, motor, and association areas

cortex

gray matter (unmyelinated), cell bodies and dendrites, information processing

inner portion

mostly white matter (myelinated), axons that connect various parts of the brain

gyrus (gyri)

ridges of tissue

sulcus (sulci)

furrows, dips

fissure

deep sulci

longitudinal fissure

separates hemispheres

right hemisphere

emotional processing, visual-spatial tasks (e.g., facial recognition)

left hemisphere

language, decision making, fact recovery

corpus callosum

connects the two, large bands of white matter forming the roof of lateral ventricles

sensory areas of the cerebrum

afferent neurons from sensor organs

motor areas of the cerebrum

efferent neurons control voluntary movement

association areas

link sensory and motor areas

→ e.g., language

central sulcus

lies between the frontal and parietal lobes and runs across the top and lateral side of each hemisphere

→ structural, not functional area

→ boundary of somatosensory and somatomotor cortex

primary motor cortex

runs anterior to the precentral gyrus, posterior frontal lobe

→ motor areas control skeletal muscle

→ decision-making and planning

primary sensory cortex

runs posterior to the precentral gyrus, anterior parietal lobe

→ receives information from sensory structures in the skin (e.g., pain, temperature, touch)

→ proprioception: sense position, movement, location

occipital lobe

→ houses the primary visual center in the posterior region

→ first to receive visual input and involves regions of temporal and parietal lobes

→ function: processes and integrates visual signals (e.g., color, object movement, orientation, depth, position)

temporal lobe

→ located along the lateral side of the brain

→ functions: short-term memory, speech, musical rhythm, some smell recognition

→ wernicke’s area

wernicke’s area

located in the left temporal lobe that is responsible for the ability to understand language

parietal lobe

posterior to frontal lobes and precentral gyrus

→ integrates sensory input (e.g., pain, touch, temperature, vibration)

→ identify objects: looking at appliances and knowing what room you are in

→ spatial relationships: where our body is relative to our surrounding objects and environment

→ proprioception

frontal lobe

most anterior lobe and the largest that runs anteriorly to the central sulcus

→ planning and executing movement and complex functions

→ motor functions (e.g., walking and running) - cerebellum involved with fine-tuning movements

→ problem-solving and decision-making

→ personality characteristics and social behavior

→ impulse control

→ broca’s area

broca’s area

→ dominant hemisphere is often the left

→ ability to produce clear, fluent speech sounds, connections between what one wants to say, and formulating the words

→ if damaged, people often speak in short, simple sentences that convey correct content, but no articles and prepositions to complete them grammatically

→ involved in comprehension and reading understanding

insula

2% of cerebral surface area and responsible for emotions and visceral response

limbic system

ring of forebrain structure surrounding the brainstem

→ consists of the amygdala

→ behavioral and emotional responses, motivation, survival, fight or flight

→ neurotransmitter: dopamine

amygdala

filters afferent sensory information and interprets it in the context of emotional and survival needs

role of dopamine

activates a pleasurable (feel good) feeling and stimulates the motivation to learn and try new things

→ different substances, including drugs, and certain activities can stimulate dopamine-releasing pathways

• exercise, activities

• certain foods like chocolate

  • drugs (alcohol, nicotine, opiates, amphetamines, and cocaine)

spinal cord

inside vertebrae (from the base of the brain, foramen magnum to the second lumbar vertebra)

→ function: connect periphery and brain (afferent and efferent), spinal reflexes

→ structure: central canal surrounded by H-shaped gray matter (reaches the dorsal surface), white matter surrounds gray matter

tract

collection of axons with a common origin and destination

→ white matter conducts impulses to and from the brain

→ name often tells something about the origin or destination (e.g., optic tract, olfactory tract)

→ ascending tracts: up to the brain

→ descending tracts: down from the brain

→ columns are groups of tracts

spinal cord damage

results in transmission problems between the brain and body

protection of the CNS

→ bone

→ three connective tissue layers (meninges)

→ cerebrospinal fluid (CSF)

→ blood-brain barrier

three connective tissue layers (meninges)

→ dura mater - outer

→ arachnoid - middle

→ pia mater - inner

cerebrospinal fluid (CSF)

produced by the choroid plexus and circulates in subarachnoid space (between the arachnoid and pia mater)

→ also found in the central canal of the cord and ventricles/connections in the brain

blood brain barrier

tight junctions between capillaries regulate the exchange between blood and CNS

drugs

a substance that has a physiological or psychological effect when ingested

prescribed drugs

25% alter psychological conditions, and almost all abused drugs affect mood

drug effects on neurotransmitters

synthesis, transport, storage, release, breakdown, reuptake

receptor site

drugs act at specific locations

receptor affinity

determines how well the drug interacts with the cell

agonist

binding causes effect in target same as the normal activating molecule

antagonist

binding blocks binding of normal effect molecule

length of effect

receptor affinity and circulating concentration of drug

ability of drugs

only alter endogenous functions or processes

effect of drugs

what occurs as a result of administration, measured relative to initial physiological conditions pre-drug

action of drugs

where and how the effect is produced

location of drugs - extracellular

minority (heparin, antacids, chelators)

location of drugs - intracellular

most drugs, receptor involved, selective and reversible

drug delivery

transported in the blood (soluble in plasma or binds proteins such as albumin), and the majority need to interact with cells

physical dependence on drugs

causes physiological changes that result in withdrawal symptoms when the drug use discontinued

→ e.g., heroin, tobacco, alcohol, barbiturates

drug addiction

compulsive use of a drug: lose control over not taking the drug despite the negative effects the drug has

true or false: you can suffer withdrawal without addiction and have addiction without suffering from withdrawal

true

atropine

→ cold medications - reduce secretions

→ dilate pupils

→ low dose slows the heartbeat

→ high dose treats slow heartbeat (bradycardia)

digitalis

stimulates heart contractions and cardiac output (congestive heart failure)

paregoric

from opium poppy, treats diarrhea

extract of ergot (fungus)

stimulates uterine contractions

cocaine

stimulates reward pathway but can also cause physical effects such as fast heart rate, sweating, and higher body temperature

strychnine binds to postsynaptic receptors

→ pest poisons

→ blocks normal IPSP transmission (antagonist)

→ muscle spasm, convulsions, death

tetanus prevents presynaptic release of inhibitory neurotransmitter

→ continued stimulation

→ effects like strychnine but different cause