BBH 203 Exam 3

What are the four motor system divisions?

- Volition

- Motor planning/ sequencing/ action selection

- activation of movement (pyramidal tracts and extra pyramidal tracts)

- Feedback/ refinement/ termination

Upper motor (1°) neurons (UMNS)

- pyramidal tracts

- UMN cell bodies located in cortical motor areas (Primary motor cortex)

How are UMNs organized?

- Primary cortex and other motor cortical areas are somatotopically organized (motor homunculus is very similar to the somatosensory homunculus)

Lower motor (2°) neurons (LMNs)

- receive input from UMNs or from 1° somatosensory neurons via reflex arcs

- provide the only input to skeletal muscles to effect contraction

- located in brainstem and spinal cord

- axons projected into cranial or spinal nerves

Pyramidal tracts

initiate voluntary motor activity, partially skilled movements

Corticospinal tract (CST)

- particularly involves with voluntary movement of distal extremities via spinal nerves

Corticobulbar tract (CBT)

- controls voluntary movement of head and neck muscles

CBT and CST

- both pyramidal tracts since the majority of their UMN axons pass through the medullary pyramids

- extrapyramidal tracts control unconscious, reflexive, and responsive aspects of movement

UMN

- 90% of axons decussate in the medulla

- cell bodies in the motor cortex bypassing the thalamus

LMN

- UMN axons synapse on LMN cell bodies in the ventral horn of the spinal cord

- LMN axons project through ventral roots into spinal nerves

Amyotrophic lateral sclerosis (ALS)

- Degenerations of corticospinal (and corticobulbar) UMNs and LMNs

- etiology (cause) is unknown in most cases (5-10% is hereditary)

- signs include weakness and ultimately paralysis

Spinal cord injury (SCI)

- usually results form an accident

- variable neurological findings

- a total sectioning of the spinal cord will result in bilateral paralysis of the body below the level of the injury

- prognosis is variable

- spinal cord regeneration can be impaired by glial scarring (astrocytes proliferate and produce scar tissue)

Motor unit

- axon of single lower motor neuron (LMN)

- all the skeletal muscle fibers it innervates

Neuromuscular junction and steps

- a chemical synapse between a single LMN axons terminal and single skeletal muscle fiber

- STEPS-

1. LMN release ACh

2. Muscle fiber binds ACh via nicotinic ACh receptors

3. End-plate potential in muscle induced

4. Muscle fiber contracts

Myasthenia gravis

- Antibodies produced against nicotinic ACh receptors

- results in dimised binds of ACh to nACRs at neuromuscular junction --> weaker contraction

- Signs and symptoms may include: weakness of limbs, disaphragm, facial and extraocular muscles, etc.

- signs and symptoms will worse over the day and with extended muscle use

- treatments include immunosuppressant drugs and removal of thymus

Reflexes

- involuntary, stereotypical motor output elicited in response to sensory input

- reflexes are mediates along sensorimotor arcs

- require only 1) sensory input; 2) local spinal cord/ brainstem circutry; 3) motor output

- can be modulated by upper motor neurons in brain

Steps of motor system

1. volition (sometimes resulting from sensory input)

2. Motor planning/ sequencing/ action selection

3. activation of movement (pyramidal system and extrapyramidal system)

4. feedback/ refinement/ termination

Basal ganglia

- functionally related group of interconnected deep-brain nuclei

- involved in planning, maintenance, and sequencing of voluntary and habitual movements

Cerebellum

- "little brain" located dorsal to brainstem

- coordinates/ refines/ sequences motor outputs (feed-forward and feedback)

- Makes adjustments to movements with respect to timing and targeting

- maintains muscle tone and regulates balance and equillibrium

Supplementary motor area

- involved in managing complex sequence of movements

- communicated with PMC, basal ganglia, and cerebellum

Premotor cortex

- functions as a "buffer" for motor program until primary motor cortex implements it

- communicates with PMC, basal ganglia, and cerebellum

Huntington's disease

- Basal ganglia disorder

- neurodegeneration of the caudate nucleus (progressive cortical atrophy)

- autosomal dominant --> onset usually in 20-30, life expectancy about 20 years following diagnosis

- treatments with antipsychoticts and antidepressants, but no cure

- hyperkinetic movement disorder: characterized by abnormal involuntary movements

- Main sign/ symptom: choreoathetosis: brief, repetitive muscle jerks and twisting/ writhing movements

Common signs of cerebellar disorders

- ataxia: loss of coordination of voluntary movement

- nystagmus: eye movement

- intention tremor: slow, rhythmic tremor occurring at the end of a planned speech movement --> ex: scanning speech

Apraxia

- the inability to intiate specific learned movements (dyspraxia is a less severe gradation)

- ideomotor apraxia: involves the inability to translate an idea into movement, despite being able to conceptualize the necessary steps (can conceptualize, but can't do)

- ideational apraxia: the inability to conceptualize movements (can't conceptualize)

Homeostasis

- the tendency to maintain internal equilibria optimal for physiological function

Biological drive

- any departure from a homeostatic set-point motivates this

- these drives are based on the principle of negative feedback (ex: thermostat)

- set points represent a range that may vary of the course of the day

Allostasis

- the adjustment of homeostatic set-points (within limits) to meet specific behavioral and/ or physiological demands

- ex: flight from pitt to denver --> over a couple days, the body would adjust to the elevation (might be difficult to breathe when you land, but then it would become easier)

What does the hypothalamus mediate?

- mediates homeostasis, controlling the autonomic nervous system and the endocrine system

- with parts of the limbic system it regulates biological drives (ex: food intake and thirst)

Autonomic nervous system

- a division of the peripheral nervous system devoted to maintaining homeostasis (nervous system's autopilot)

- involuntary and unconscious

- regulated by the hypothalamus, brainstem, and spinal cord

How is the autonomic nervous system divided?

- Connects CNS with internal organs

- Efferent limb: smooth muscle, cardiac muscle, glands, adipose tissue

- Afferent limb: chemoreceptors, baroreceptors (sometimes the ANS is treated as exclusively efferent)

ANS divisions

- sympathetic division: fight or flight, exits CNS at thoracic and upper lumbar spinal cord

- Parasympathetic division: rest and digest or feed and breed, exits CNS at brainstem and sacral spinal cord

- enteric division: regulates GI mobility and secretion, modulated by sympathetic and parasympathetic divisions

- organs/ tissues are dually innervated by sympathetic and parasympathetic divisions

Why do we have both and autonomic nervous system and endocrine system?

- autonomic nervous system can operate on a faster time scale than the endocrine system, if you needed to sustain a threat, cortisol would still be making you feel stressed after the immediate threat

- release of hormones linger, if you needed to sustain this, hormone release from the endocrine system would be adaptive

Thermoregulation: heat loss center

- anterior hypothalamic nuclei and preoptic area comprise the heat loss center

- triggers sweating and cutaneous vasodilation, lowers Basal metabolic rate to lower body temperature

- damage can lead to hyperthermia (overheating)

Thermoregulation: heat conservation center

- posterior hypothalamic nuclei comprise the heat conservation center

- triggers shivering, cutaneous vasoconstriction, a piloerection, raises BML to raise body temperature

- damage can lead to poikilothermia ( hypothermia and hyperthermia simultaneously)

Osmotic thirst

- loss of cytoplasmic volume (intracellular), which is related to increased extracellular osmolarity (amount of solute dissolved)

Hypovolemic thirst

Loss of blood plasma volume (extracellular)

Neural regulation of osmotic thirst

- circumventricular organs of the brain (outside of the BBB) detect changes in osmolarity of blood plasma

- hypothalamus release vasopressin

Neural regulation of hypovolemic thirst

1. baroreceptive stretch information from cardiac artrties is relayed to the hypothalamus

2. renin-angiotensin system constricts blood vessels to maintain blood pressure

(both systems promote thirst and vasopressin is released)

Feeding and satiety centers

Hunger and associated metabolic changes regulated in hypothalamus by

- Acrcuate nucleus: master food intake control

- lateral hypothalamus: feeding initiation

- paraventricular nucleus

-ventromedial hypothalamus: satiety

What are the hunger promoting and satiety promoting peptides?

- ghrelin: hunger-promoting peptide (Gosh, I am hungry!)

- leptin: satiety- promoting peptide (Lovely, I am full!)

Hypothalamic dysregulation: leptin

- absence of circulating leptin results in obesity, diabetes, and sterility

- ventromedial hypothalamic syndrome: lesion or malformation of ventromedial nuclei leads to hyperphagia (eating too much), obesity, rage attacks, increased sleep

Obesity

may involve serotonin dysregulation in certain people

Anorexia nervosa

- abnormal ghreline signaling

- pervasive grey matter deficits

- dysfunction in limbic and association cortex reduced connectivity thereof

Bulimina nervosa

- Higher ghrelin signaling between meals (likely reflecting hunger)

- PYY fails to rise adequately following eating

Suprachiasmatic nucleus

- master clock of the body

- entrains physiological properties around a circadian schedule

- receives input from retinal ganglia cells

What does the SCN promote and where?

SCN promotes melatonin secretion from the pineal gland (lesion of SCN = dysregulation of circadian rhythms)

HELPFUL TO REMEMBER --> car picture with pneumonics

look at car pneumonic to help remember homestasis stuff (homeostasis powerpoint)

What does the brain's reward circuitry contribute to?

- decision maing by assigning incentive salience (positive motivation, sense of wanting) to stimuli, events, or outcomes

- associative learning

- pleasure-based emotions

--> if reward is a homeostatic drive, it is distinct to the drives essential to our survival

Intracranial self-stimulation

- Olds and Milner: rats implanted with electrodes in various parts of their brain

- When rats get specific implantations delivering current to specific brain regions, they learned to continue pressing the lever

- there must have been some reward or sense of pleasure from repeatedly pressing the lever

liking versus wanting

- liking: deriving pleasure

- wanting: incentive salience

wanting network

brain regions connected via the mesolimbocortical pathway

Mesolimbocortical pathway

- dopaminergic pathway

- originates in Ventral tegmental area (VTA) and terminates in nucleus accumbens (NAc)

- dopamine binds here during "wanting"

Tolerance

repeated exposure to the same dose of a drug resulting in a lesser effect

Physical dependence

- physiological adaptations resulting from drug use

- results in withdrawal syndrome: a set of symptoms that appear after drug use is discontinued (ex: tremors, delirium)

Psychological dependence/ behavioral dependence

- defined based on observable behavior

- indications: frequency of using the drug, time or effort in drug-seeking behaviors, tendency to relapse, reports of craving the drug

what can behavioral dependence result from?

- may result from reinforcement (can be positive or negative)

- reinforcement leading to drug re-use: reward (positive), fear or discomfort (negative)

Drug (substance) abuse

the intentional and inappropriate use of a drug resulting in physical, emotional, financial, intellectual, or social consequences for the user

Drug addiction

- the most severe form of drug abuse

- definition is controversial

- user experiences profoundly negative consequences affecting every aspect of life

- affects body and brain

Substance use disorder (DSM 5)

encompasses addiction (severe SUD ~ addiction)

Drug tolerance vs dependence vs addiction

- if you're dependent on a drug, you are said to be addicted

- if you develop tolerance, you might not necessarily be addicted

- when tolerance gets high enough, that might lead to dependence

euphoria

- all psychoactive drugs induce this pleasure

- euphoria is a pleasurable feeling that is hard to reach without drugs

Severe dependence/ addiction

- leads to anhedonia (inability to experience pleasure) and dysphoria (intense sense of dread/ dissatisfaction) --> both lead to increased activity in the amygdala

- hypofrontality: decreased activity, structural changes in prefrontal cortex

Options for addiction recovery

- pharamacological treatments often combined with therapy and lifestyle changes

- neurological changes sometimes completely reversible with prolonged drug abstention

conspecific

- member of your own species

- can be a prereq for sexual desire

neural correlates of attraction

- nucleus accumbens (NAcc)

- anterior cingulate cortex (Acc)

- medial orbitofrontal cortex

How universal are parameters of human attractiveness

- parameters of attractiveness can vary across cultures and over time

- constants across cultures drive sexual selection (natural selection involving people with certain traits having more success reproducing)

- study with 3-6 month olds: helped formed the conclusion that there have to be biological correlates viewed as attractive that don't have to do with culture

Physical paramteters of attractiveness

- facial symmetry

- youthful female features (straight men)

- masculine features (straight women) --> less masculine features preferred for long-term relationships

Major histocompatibility complex (MHC)

- differences in MHC genes may underlie the olfactory component of attraction

- this stems from the idea that different body odors would correlate with not being closely related --> closely related people having offspring would cause problems

Sexual desire

- greater registration of pleasant somatosensory experiences, higher activity in posterior insula

romantic love

- greater cognitive valence, higher activity in the anterior insula

Oxytocin

- both real-time sexual desire and romantic love increase mesolimbocortical pathway activity

- oxytocin and vasopresin release from the posterior pituitary gland

What is sexual desire not exclusively determined by?

- sexual desire is not exclusively determined by biology

- it is also predicated on sociocutural factors, interpersonal and gender dynamics, mental and physical health, general sexual interest

Sexual desire in women

- positively correlated with estrogen

- negatively correlated with progesterone

- this occurs because estrogen levels peak at ovulation which is the most likely time to be fertile

Why does sexual desire decrease during and beyond menopause?

- lubrication

- change of pain modulation of sex

Sexual desire in men

- normal testosterone levels correlated with baseline sexual desire in younger men

- sexual desire and testosterone tend to increase in situations of competition and decrease when men enter committed relationships or become parents

Monogamy

- oxytocin and vasopresin are also thought to play a role in promoting monogamy

- monogamy: ales take a single female as their one lifelong partner

polygamy

- more than one partner

- human men are capable at producing many offspring at low cost

- less sexual selectivity

- offset by parental investment because won't be able to dedicate time to all children

- human females experience high reproductive costs

Four stages of reproductive behavior

1. sexual attraction

2. appetitive behavior

3. copulation

4. postcopulatory behavior

Neural bases of copulation in humans

- different brain networks prevail in male and female brains prior to orgasm, very similar networks coalesce during during orgasm

Central pattern generators

- circuits that receive unpatterened input and output it as patterned output of the spinal cord

- works with the autonomic nervous system during orgasm

Sexual dimorphism

- the condition in which there are (typically non-reproductive) anatomical differences between the sexes (ex: lions have manes)

- male human brains are are 11% larger than female brains on average --> when controlling for body size, no human brain region but one differs by more than 1% in size between males and females

- INAH-3: a nucleus in the anterior hypothalamus that is 1.6X larger in men than women

what accounts for average differences in behavior between men and women?

- hormones and socialization

sexual orientation

- a stable pattern of attraction to members of one or more genders

sexual orientation genetic correlates

around 50% heritable in sexual orientation is accounted by genetics based on twin studies

sexual orientation hormonal correlates

fetal androgen (male hormone) exposure seems to be higher on average for lesbians than straight women

sexual orientation neural correlates

- INAH-3 of hypothalamus seems to be larger in higher in straight men than gay men

- differences in grey matter volumes between people of different sexual orientations

cross-shift hypothesis

gay men and women exhibit similar cognitive patterns ro straight women and men respectively (evidence to support this so far is mixed, data lacking for bisexual people)

gender identity

- one's self concept of being male, female, or non-binary

- transgender people identify with a gender other than their biological sex, as assigned at birth

- neural correlates of gender identity poorly understood

- evidence to date suggests certain area more closely resembled preferred gender not natal (birth) gender